Display apparatus, liquid crystal display apparatus and driving method for display apparatus

ABSTRACT

A display apparatus is constituted by a display device including a plurality of pixels and control means for effecting a plurality of displaying operations at each pixel. Each of the displaying operation includes at least a first operation for displaying a first image at a first luminance and a second operation for displaying a second image substantially identical to the first image at a second luminance, said first and second luminances being non-zero and different from each other. One of the first and second luminances may preferably be smaller than ⅕ of the other luminance.

FIELD OF THE INVENTION AND RELATED ART

[0001] The present invention relates to a display apparatus,particularly by a liquid crystal display apparatus including a liquidcrystal device for use in light-valves for flat-panel displays,projection displays, printers, etc., and a driving method for the(liquid crystal) display apparatus.

[0002] As a type of a nematic liquid crystal display device usedheretofore, there has been known an active matrix-type liquid crystaldevice wherein each pixel is provided with an active element (e.g., athin film transistor (TFT)).

[0003] As a nematic liquid crystal material used for such an activematrix-type liquid crystal device using a TFT, there has been presentlywidely used a twisted nematic (TN) liquid crystal as disclosed by M.Schadt and W. Helfrich, “Applied Physics Letters”, Vol. 18, No. 4 (Feb.17, 1971), pp. 127-128.

[0004] In recent years, there has been proposed a liquid crystal deviceof In-Plain Switching mode utilizing an electric field applied in alongitudinal direction of the device, thus improving a viewing anglecharacteristic being problematic in TN-mode liquid crystal displays.Further, a liquid crystal device of a super twisted nematic (STN) modewithout using the active element (TFT etc.) has also be known as arepresentative example of the nematic liquid crystal display device.

[0005] Accordingly, the nematic liquid crystal display device includesvarious display or drive modes. In any mode however, the resultantnematic liquid crystal display device has encountered a problem of aslow response speed of several ten milliseconds or above.

[0006] In order to solve the above-mentioned difficulties of theconventional types of nematic liquid crystal devices, a liquid crystaldevice using a liquid crystal exhibiting bistability (“SSFLC”, SurfaceStabilized FLC), has been proposed by Clark and Lagerwall (JapaneseLaid-Open Patent Application (JP-A) 56-107216, U.S. Pat. No. 4,367,924).As the liquid crystal exhibiting bistability, a chiral smectic liquidcrystal or a ferroelectric liquid crystal (FLC) having chiral smectic Cphase (SmC*) is generally used. Such a chiral smectic (ferroelectric)liquid crystal has a very quick response speed because it causesinversion switching of liquid crystal molecules by the action of anapplied electric field on spontaneous polarizations of their liquidcrystal molecules. In addition, the chiral smectic liquid crystaldevelops bistable states showing a memory characteristic and further hasan excellent viewing angle characteristic. Accordingly, the chiralsmectic liquid crystal is considered to be suitable for constituting adisplay device or a light valve of a high speed, a high resolution and alarge area.

[0007] In recent years, as another liquid crystal material, anantiferroelectric liquid crystal showing tristability (tristable states)has caught attention. Similarly as in the ferroelectric liquid crystal,the antiferroelectric liquid crystal causes molecular inversionswitching due to the action of an applied electric field on itsspontaneous polarization, thus providing a very high-speedresponsiveness. This type of the liquid crystal material has a molecularalignment (orientation) structure wherein liquid crystal moleculescancel or counterbalance their spontaneous polarizations each otherunder no electric field application, thus having no spontaneouspolarization in the absence of the electric field.

[0008] The above-mentioned ferroelectric and antiferroelectric liquidcrystal causing inversion switching based on spontaneous polarizationare liquid crystal materials assuming smectic phase (chiral smecticliquid crystals). Accordingly, by using these liquid crystal materialscapable of solving the problem of the conventional nematic liquidcrystal materials in terms of response speed, it has been expected torealize a smectic liquid crystal display device.

[0009] As described above, the (anti-)ferroelectric (or chiral smectic)liquid crystal having a spontaneous polarization has been expected to besuitable for use in displays exhibiting a high-speed responseperformance in the near future.

[0010] In the case of the above-mentioned device (cell) using the(anti-)ferroelectric liquid crystal exhibiting bistability ortristability, however, it has been difficult to effect a gradationdisplay in each pixel based on its display principle.

[0011] In recent years, in order to allow a mode of controlling variousgradation levels, there have been proposed liquid crystal devices usinga specific chiral smectic liquid crystal, such as a ferroelectric liquidcrystal of a short pitch-type, a polymer-stabilized ferroelectric liquidcrystal or an anti-ferroelectric liquid crystal showing no threshold(voltage) value. However, these devices have not been put into practicaluse sufficiently.

[0012] On the other hand, with respect to a liquid crystal displayapparatus, it has been clarified by recent studies that it is difficultto attain a sufficient human-sensible high-speed motion picture responsecharacteristic only by simply increasing a response speed of a liquidcrystal portion of a conventional liquid crystal device (using a nematicTN or STN) mode)(as described in, e.g., “Shingaku Giho” (TechnicalReport of IEICD), EID 96-4 (1996-06, p. 19).

[0013] According to results of these studies, it has been concluded thata scheme wherein a time aperture (opening) rate is decreased to at most50% by using a shutter or a double-rate display scheme is effective inimproving motion picture qualities as a scheme by which a human-sensiblehigh-speed motion picture responsiveness is provided.

[0014] However, in the conventional nematic (display) mode, the responsespeed of a liquid crystal is insufficient, thus failing to be applied tothe above motion picture display schemes. Further, in order to realizethe high-speed motion picture display as described above by using theconventionally proposed high-speed responsive chiral smectic liquidcrystal devices including those using a ferroelectric liquid crystal ofa short pitch-type or a polymer-stabilized type and a threshold-lessantiferroelectric liquid crystal, any (chiral) smectic mode isaccompanied with difficulties, such as complicated driving method andperipheral circuits, thus leading to an increase in production cost.Even when a time aperture rate is completely set to 50% or below, theentire display device (apparatus) is also correspondingly decreased inbrightness of 50% or below. As a result, it is clear that the resultantdisplay device causes a lowering in (display) luminance.

[0015] In recent years, it has been desired to effect full-color displayusing a liquid crystal device. As one of methods for effectingfull-color display, there has been known a method wherein a liquidcrystal device is irradiated with respective color lights (e.g., redlight, green light and blue light) in succession to effect switching ofliquid crystal molecules under the respective color light irradiations.Even in such a liquid crystal device, however, if the time aperture rateis decreased to at most 50% as described above, the resultant liquidcrystal device is similarly accompanied with a (display) luminancelowering problem.

[0016] More specifically, FIG. 19 is a block diagram of a conventionalliquid crystal apparatus.

[0017] Referring to FIG. 19, the liquid crystal apparatus includes aliquid crystal device (panel) 80, a color light source 101 capable ofemitting respective color lights (of red (R), green (G) and blue (B))and a color light source driving unit 102 for driving the color lightsource 101 based on synchronizing signals.

[0018] The liquid crystal device 80 shown in Figure 19 includes 480scanning lines supplied with scanning (data) signals X001 to X480,respectively, through a Y-driver 92. These X— and Y-drivers 91 and 92are driven by applying a drive voltage carrying drive signals. Thesynchronizing signals supplied to the color light source driving unitare separated from the drive signals.

[0019]FIG. 20 is a time chart for illustrating a driving method of theconventional liquid crystal apparatus shown in FIG. 19.

[0020] Referring to FIG. 20, when the liquid crystal apparatus isdriven, one frame period F0 is divided into three field periods F1, F2and F3. In this instance, when a frame frequency is set to 60 Hz, oneframe period F0 is ca. 16.7 msec. and each of the field period F1, F2and F2 is ca. 5.5 msec. The liquid crystal device 80 is irradiatedsuccessively with the respective color lights (R, G, B) from the colorlight source 101 in the field periods F1, F2 and F3, respectively (FIGS.20(a), (b) and (c)). In each of the field periods F1, F2 and F3, withrespect to each of scanning lines (S001 to S048), a black and white(monochromatic) image (for R in F1, for G in F2 or for B in F3) issuccessively displayed in a prescribed display period (RD, GD or BD) asshown in FIG. 20(d). As a result, these resultant (color) images arevisually color-mixed to be recognized as a desired full-color image.

[0021] According to such a liquid crystal apparatus, it is not necessaryto provide the liquid crystal device 80 with a color filter, thusobviating problems due to the formation of the color filter, such as alowering in production yield, an attenuation (lowering in luminance) ofillumination light at the color filter and an increase in quantity oflight of a backlight (light source) for preventing the lowering inluminance. On the other hand, however, the image display period (Rd, GDor BD) is half of the corresponding field period (F1, F2 or F3), thusresulting in an about half utilization of the color light source 101.Accordingly, the resultant luminance is lowered in spite of noattenuation of the illumination light by the use of the color filter, sothat the color light source 101 is required to provide a higherluminance in order to prevent the lowering in luminance of the liquidcrystal device 80.

[0022] In the case where such a liquid crystal device 80 uses aferroelectric liquid crystal (e.g., a liquid crystal assuming chiralsmectic C phase), it is necessary to apply a reset pulse (voltage) incombination with a writing pulse. Even when the reset pulse is set tohave a negative polarity and the writing pulse is set to have a positivepolarity, the resultant writing pulse becomes smaller depending ondisplaying gradation levels in some cases, thus resulting in DC voltagecomponent applied to the liquid crystal to cause an occurrence ofso-called burning or sticking.

SUMMARY OF THE INVENTION

[0023] In view of the above-mentioned problems, an object of the presentinvention is to provide a display apparatus, particularly a liquidcrystal display apparatus, capable of effecting gradation control withhigh-speed responsiveness while ensuring a practical brightness toimprove motion picture image qualities without using a complicatedcircuit.

[0024] Another object of the present invention is to provide a drivingmethod for the (liquid crystal) display apparatus.

[0025] According to the present invention, there is provided a displayapparatus, comprising:

[0026] a display device including a plurality of pixels, and

[0027] control means for effecting a plurality of displaying operationsat each pixel, each displaying operation including at least a firstoperation for displaying a first image at a first luminance and a secondoperation for displaying a second image substantially identical to thefirst image at a second luminance, said first and second luminancesbeing non-zero and different from each other.

[0028] According to the present invention, there is also provided aliquid crystal display apparatus, comprising:

[0029] a liquid crystal device including a layer of liquid crystal, apair of substrates disposed to sandwich the liquid crystal, and apolarizer disposed on at least one of the substrates, at least one ofthe substrates being provided with an alignment film for aligning theliquid crystal in contact therewith, the pair of substrates respectivelyhaving thereon mutually intersecting electrodes for applying a voltageto the liquid crystal thereby forming a matrix of pixels each at anintersection of the electrodes on the pair of substrate, and

[0030] control means for effecting a plurality of displaying operationsat each pixel, each displaying operation including at least a firstoperation for displaying a first image at a first luminance and a secondoperation for displaying a second image substantially identical to thefirst image at a second luminance, said first and second luminancesbeing non-zero and different from each other.

[0031] According to the present invention, there is further provided aliquid crystal apparatus, comprising:

[0032] a liquid crystal device including a layer of liquid crystal, apair of substrates disposed to sandwich the liquid crystal, and apolarizer disposed on at least one of the substrates, at least one ofthe substrates being provided with an alignment film for aligning theliquid crystal in contact therewith, the pair of substrates respectivelyhaving thereon mutually intersecting electrodes for applying a voltageto the liquid crystal thereby forming a matrix of pixels each at anintersection of the electrodes on the pair of substrate,

[0033] a light source provided to one of the substrates for emittinglight to be optically modulated by the liquid crystal device, and

[0034] control means for effecting a plurality of illuminatingoperations including at least a first operation for displaying a firstimage by turning the light source on at a first illuminance and a secondoperation for displaying a second image substantially identical to thefirst image by turning the light source on at a second illuminance, saidfirst and second illuminances being non-zero and different from eachother.

[0035] The present invention provides a liquid crystal apparatus,comprising:

[0036] a liquid crystal device including a layer of liquid crystal, apair of substrates disposed to sandwich the liquid crystal, and apolarizer disposed on at least one of the substrates, at least one ofthe substrates being provided with an alignment film for aligning theliquid crystal in contact therewith, the pair of substrates respectivelyhaving thereon mutually intersecting electrodes for applying a voltageto the liquid crystal thereby forming a matrix of pixels each at anintersection of the electrodes on the pair of substrate, and

[0037] voltage application means for applying a voltage to the liquidcrystal through the electrodes, wherein

[0038] the liquid crystal has an alignment characteristic such that theliquid crystal is aligned to provide an average molecular axis to beplaced in a monostable alignment state under no voltage application, istilted from the monostable alignment state in one direction whensupplied with a voltage of a first polarity at a tilting angle whichvaries depending on magnitude of the supplied voltage, and is tiltedfrom the monostable alignment state in the other direction when suppliedwith a voltage of a second polarity opposite to the first polarity at atilting angle, said tilting angles providing maximum tilting anglesformed under application of the voltages of the first and secondpolarities, respectively, different from each other.

[0039] The present invention also provides a liquid crystal apparatus,comprising:

[0040] a liquid crystal device including a layer of liquid crystal, apair of substrates disposed to sandwich the liquid crystal, and apolarizer disposed on at least one of the substrates, the pair ofsubstrates respectively having thereon mutually intersecting electrodesfor applying a voltage to the liquid crystal thereby forming a matrix ofpixels each at an intersection of the electrodes on the pair ofsubstrate, and

[0041] a drive circuit for driving the liquid crystal device to effectdesired gradational display based on change in emitting light quantityfor each pixel, wherein each pixel is supplied with a driving signalfrom said drive circuit, said driving signal including in a first perioda voltage of a first polarity for providing a prescribed light quantityequal to or larger than a light quantity for providing a prescribedgradational image and in a second period a voltage of a second polarityopposite to the first polarity for providing a second light quantitysmaller than the prescribed light quantity but larger than zero, therebyto effect desired gradational display through the first and secondperiod.

[0042] The present invention further provides a driving method for adisplay apparatus wherein a plurality of color lights are successivelyemitted from a color light source and in synchronism with the respectivelight emissions, switching of the respective lights is effected by adisplay device to visually color-mixing the respective lights to providea full-color image, said driving method comprising:

[0043] dividing one frame period into a plurality of field periods andfurther dividing each field period into a plurality of sub-fieldperiods,

[0044] changing a color of a light emitted from the color light sourcefor each field period, and

[0045] displaying a higher luminance image in at least one sub-fieldperiod in each field period and a lower luminance image in at least oneanother sub-field period in each field period.

[0046] These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIGS. 1A an 1B are illustrations of liquid crystal molecules and asmectic layer structure formed thereby in C1 alignment and C2 alignment,respectively, in an SSFLC-type device.

[0048]FIGS. 2A and 2B are illustrations of positions of C-directors inthe C1 alignment shown in FIG. 1A and the C2 alignment shown in FIG. 1B,respectively.

[0049]FIGS. 3A and 3B are illustrations of courses of smectic layerformation of liquid crystal molecules exhibiting a phase transitionseries of Ch (cholesteric phase)-SmA (smectic A phase)-SmC* (chiralsmectic C phase) in an SSFLC-type device and a phase transition seriesof Ch-SmC* in an embodiment of a liquid crystal device used in thepresent invention, respectively.

[0050] FIGS. 4A, 4BA, 4BB, 4CA and 4CB are illustrations of alignmentstates of liquid crystal molecules in an embodiment of a liquid crystaldevice used in the present invention, wherein FIG. 4A shows a course ofsmectic layer formation of liquid crystal molecules exhibiting a phasetransition series of Ch-SmC* in a chevron structure or an obliquebookshelf structure, FIGS. 4BA and 4CA are plan views showing alignmentstates of liquid crystal molecules having a chevron structure in a C1alignment and a C2 alignment, respectively, and FIGS. 4BB and 4CB arecorresponding positions of liquid crystal molecules and C-directors inthe alignment states shown in FIGS. 4BA and 4CA, respectively.

[0051]FIG. 5 is a schematic view showing an alignment state of liquidcrystal molecules in chiral smectic C phase.

[0052] FIGS. 6AA, 6AB, 6BA, 6BB, 6CA, 6CB and 6D are schematic viewsshowing a liquid crystal inversion behavior in chiral smectic C phaseunder voltage application in an embodiment of a liquid crystal deviceused in the present invention, wherein FIGS. 6AA, 6BA and 6CA are planviews showing alignment states of liquid crystal molecules in C2alignment; FIGS. 6AB, 6BB and 6CB are corresponding positions of liquidcrystal molecules and C-directions in the alignment states shown inFIGS. 6AA, 6BA and 6CA, respectively; and FIG. 6D illustrates anarrangement of a pair of polarizers.

[0053]FIG. 7 is a graph showing an example of a V-T(voltage-transmittance) characteristic of a liquid crystal device usedin the present invention.

[0054]FIGS. 8A and 8B are illustrations of states of energy potentialsof an SSFLC in C1 alignment and C2 alignment, respectively.

[0055]FIGS. 9A and 9B are illustrations of states of energy potentialsof a liquid crystal materials in a liquid crystal device used in thepresent invention in C1 alignment and C2 alignment, respectively.

[0056]FIG. 10 is a schematic sectional view of an embodiment of a liquidcrystal device used in the present invention.

[0057]FIG. 11 is a schematic plan view of an embodiment of an activematrix-type liquid crystal device applicable to the present invention incombination with drive circuits therefor.

[0058]FIG. 12 is an enlarged sectional view showing each pixel portionof the liquid crystal device shown in FIG. 11.

[0059]FIG. 13 shows an equivalent circuit of each pixel portion shown inFIG. 12.

[0060]FIG. 14 shows drive waveform diagrams (at (a), (b) and (c)) fordriving the active matrix-type liquid crystal device shown in FIG. 11and a corresponding transmitted light quantity (at (d)).

[0061]FIGS. 15 and 19 are block diagrams of embodiments of the liquidcrystal apparatus according to the present invention and a conventionalliquid crystal apparatus, respectively.

[0062]FIGS. 16, 17 and 21 are time charts for illustrating embodimentsof the driving method for a liquid crystal display apparatus accordingto the present invention, respectively.

[0063]FIG. 18 shows a circuit diagram of an embodiment of a backlight(color light source) used in the present invention.

[0064]FIG. 20 is a time chart for illustrating an embodiment of aconventional driving method for a liquid crystal apparatus.

[0065]FIG. 22 is a graph showing another embodiment of a V-Tcharacteristic of a liquid crystal device used in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] Hereinbelow, some preferred embodiments of the (liquid crystal)display apparatus and the driving method therefor according to thepresent invention will be described specifically with reference to thedrawings.

First Embodiment

[0067] In the display device used in the present invention according tothis embodiment, a plurality of displaying operations per second at eachpixel for the display device are effected by a control meansconstituting a display apparatus of the present invention in combinationwith the display device.

[0068] The plurality of displaying operations includes at least a firstoperation for displaying a first image at a (non-zero) higher luminance(first luminance) and a second operation for displaying a second imagesubstantially identical to the first image at a (non-zero) lowerluminance (second luminance), thus providing a human-sensible high-speedmotion picture image without largely impairing a luminance or brightnessof the resultant display device.

[0069] The display device used in the present invention may include adisplay device of a type wherein an image display is performed byoptical modulation of external light and a self-emission type displaydevice, such as an EL (electroluminescent) display device or a plasmadisplay device.

[0070] In the present invention, the display device may particularlypreferably be a liquid crystal (display) device including a pair ofoppositely disposed substrates each provided with an electrode forapplying a voltage to a liquid crystal and at least one of which issubjected to a uniaxial aligning treatment at its opposing (inner)surface and is provided with a polarizer and including a liquid crystaldisposed between the opposing surfaces of the pair of substrates.

[0071] In this embodiment, in the (liquid crystal) display device, thelower (second) luminance in the second operation may preferably be atmost ⅕ of the higher (first) luminance in the first operation.Particularly, in the liquid crystal device, the plurality of displayingoperations (optical modulation operations) may preferably be performedsuch that a first optical modulation operation is performed to provide afirst transmittance (passing through the device) corresponding to thefirst luminance for displaying the first image in a first display(sub-)field period and a second optical modulation operation isperformed to provide a second transmittance which is non-zero and atmost ⅕ of the first transmittance in a second display (sub-)fieldperiod.

[0072] In this embodiment, the (liquid crystal) display apparatus usingthe liquid crystal device may further include an external light sourceas a backlight (e.g., a white light source or a color light source)disposed outside one of the pair of substrates of the liquid crystaldevice. In this display apparatus, the liquid crystal device isilluminated with the light source at a first illuminance in at least onedisplay (sub-)field period constituting one frame period and at a secondilluminance which is non-zero and smaller than the first illuminance inat least one another (different) display ((sub-)field) period, thuseffecting the above-mentioned plurality of displaying operations.

[0073] The second illuminance may preferably be at most ⅕ of the firstilluminance.

[0074] Another driving method for such a display apparatus based onilluminance control of a color light source will be described withreference to FIGS. 15 and 21 in combination with FIGS. 11 and 12.

[0075]FIG. 15 is a block diagram of a liquid crystal display apparatus100 including a color light source 101 according to the presentinvention. The display apparatus has a structure identical to that ofthe conventional display apparatus shown in FIG. 19.

[0076] The display apparatus 100 of the present invention is driven by adriving method based on illuminance control as shown in FIG. 21.

[0077] More specifically, referring to FIG. 21, when light source lightsissued from the color light source 101 are lights of red (R), green (G)and blue (B), one frame period F0 is divided into three (first to third)field periods F1, F2 and F3 for emitting lights of R, G and B,respectively. Each of the field periods F1, F2 and F3 is further dividedinto three (firsts to third) sub-field periods 1F, 2F and 3F. In thefirst sub-field period 1F (of each of the field periods F1, F2 and F3),the color light source 101 is turned off. Then, the color light source101 is turned on in the second sub-field period 2F at a firstilluminance so as to provide a prescribed color light (e.g., red (R) inFIG. 21) (R1 illumination) and in the third sub-field period 3F at asecond illuminance, which is non-zero and smaller than the firstilluminance, so as to provide the same color light (R2 illumination),thus displaying a higher luminance (red) image in the second sub-fieldperiod 2F and a lower luminance (red) image in the third sub-fieldperiod 3F.

[0078] The thus-displayed color images different in color in the threefield periods F1, F2 and F3, respectively are visually color-mixed to berecognized as a full-color image in each frame period F0.

[0079] The number of the field periods may be changed depending on thenumber of light-source lights issued from the color light source 101.For example, when four colors (of red (R), green (G), blue (B) and white(W)) are employed as the light-source light, one frame period F0 may bdivided into four field periods F1, F2, F3 and F4.

[0080] In the above driving method, the order of light illumination isset to B, R and G. However, the light illumination order may beappropriately changed in any order (e.g. the order of R, G and B) withinone frame period.

[0081] In the above driving method, the liquid crystal device 80 is ofan active matrix-type as shown in FIGS. 11 and 12.

[0082] The driving method will be described more specifically based onFIG. 21 in combination with FIGS. 11 and 12.

[0083] Referring to these figures, in the first sub-field period 1F ofthe second field period F2, any one of gate lines G1, G2, . . . Gn(e.g., i-th gate line Gi) is supplied with a gate voltage Vg in aprescribed period (selection period Ton). In synchronism with the gatevoltage application, any one of source lines S1, S2, . . . , Sn (e.g.,j-th source line Sj) is supplied with a source voltage Vs (=Vx) in theselection period Ton relative to a potential Vc (not shown) of a commonelectrode 42 taken as a reference potential. In this instance, a TFT(thin film transistor) 94 on a pixel concerned along with the gate andsource lines Gi and Sj is turned on by the application of the gatevoltage Vg and the pixel is electrically charged by the application ofthe source voltage Vx via the TFT 94 and a pixel electrode 95 at aliquid crystal capacitor C1 c and a holding (supplementary) capacitorCs.

[0084] In a non-selection period Toff (other than Ton) in the firstsub-field period 1F of the second field period F2, the gate voltage Vgis not applied to the gate line Gi but is applied to other gate linesG1, G2, . . . , Gn (other than Gi), thus turning the TFT 94 off. As aresult, the liquid crystal capacitor C1 c and the holding capacitor Csretains the charges (stored in the selection period Ton) through thenon-selection period Toff, whereby a liquid crystal 49 is continuouslysupplied with a pixel voltage Vpix (=Vx) through the entire second fieldperiod F2, thus continuously retaining liquid crystal molecules in asubstantially identical position (through the entire second field periodF2).

[0085] Similarly, scanning (selection of the gate lines) is continued tothe last gate line Gn in the first sub-field period 1F (of the secondfield period F2) wherein all the liquid crystal molecules are maintainedin a prescribed alignment state. In the first sub-field period 1F, thecolor light source 101 is turned off, thus resulting in a transmittedlight quantity (T) of zero. If the color light source 101 iscontinuously turned on, a resultant transmitted light quantity (T) ischanged as shown at M of FIG. 21 depending on respective color lighttransmittances.

[0086] Then, the color light source 101 is turned on at a firstilluminance in a subsequent second sub-field period 2F and at a secondilluminance lower than the first illuminance but larger than zero in athird sub-field period 3F subsequent to the second sub-field period 2F,thus attaining a transmitted light quantity Tx in the second sub-fieldperiod 2F and a transmitted light quantity Ty in the third sub-fieldperiod 3F, respectively. As a result, in the entire second field periodF2, an average transmitted light quantity of zero, Tx and Ty isobtained.

[0087] In this instance, in the second field period F2, the liquidcrystal device 80 is illuminated with the color light source 101emitting red light, whereby a black-and-white (monochrome) imagedisplayed on the liquid crystal device is recognized as a red image.Similarly, in the previous (first) field period F1, a black-and-whiteimage is recognized as a blue image by blue light illumination. In thesubsequent (third) field period F3, a black-and-white image isrecognized as a green image by green light illumination. As a result,these color images are visually color-mixed to be recognized as afull-color image in the entire (one) frame period consisting of thethree field periods F1, F2 and F3.

[0088] In this embodiment, the source voltage applied to the source lineSj may preferably be changed in its polarity frame by frame (frameinversion driving scheme), whereby the liquid crystal 49 is suppliedwith a positive-polarity source voltage Vx and a negative-polaritysource voltage −Vx in an alternating manner, thus suppressing adeterioration of the liquid crystal 49.

[0089] In the case where such a frame inversion driving scheme isadopted in combination with the illuminance control of the color lightsource as shown in FIG. 21, the liquid crystal 49 used may be not onlyone exhibiting voltage-transmittance (V-T) characteristic as shown inFIG. 7 but also one exhibiting a V-T characteristic as shown in FIG. 22,thus allowing a more latitude in selection of a liquid crystal material.

[0090] As the liquid crystal device 80 more suitable for this embodimenteffecting display based on the setting of the first and secondluminances (illuminances) as described above, a liquid crystal deviceusing a chiral smectic liquid crystal assuming a monostable state underno voltage application, particularly as described in JP-A 10-177145 isused.

[0091] Hereinbelow, a liquid crystal assuming chiral smectic phasesuitably used as the liquid crystal 49 of the liquid crystal device 80used in the present invention will be described in terms of an alignmentstate in chiral smectic phase and a switching behavior of its liquidcrystal molecules by contrast with the above-mentioned conventionalSSFLC with reference to FIGS. 1-8.

[0092] In FIGS. 1-8, the alignment state and switching behavior areexplained based on typical molecular models representing relationshipsbetween liquid crystal molecules and virtual cone (defining a positionof liquid crystal molecules), a normal to a smectic (molecular) layerand an average uniaxial aligning treatment axis. The liquid crystalmolecules are present between a pair of substrates and twisted in adirection of a normal to the substrates. The behavior of the liquidcrystal molecules is optically observed (e.g., through a polarizingmicroscope) as that of an average molecular axis. Accordingly, theaverage molecular axis defined in the present invention corresponds to asingle liquid crystal molecule.

[0093] In the conventional SSFLC-type device using a liquid crystalassuming chiral smectic C phase (SmC*), liquid crystal molecules arestabilized in (either one of) two (optically) stable states, thusdeveloping a bistability or a memory characteristic. First, this memorystate will be described with reference to FIGS. 1 and 2.

[0094]FIGS. 1A and 1B are schematic illustrations of liquid crystalmolecules and a smectic (molecular) layer structure formed thereby inthe SSFLC-type device.

[0095] Referring to FIGS. 1A and 1B, a liquid crystal 13 sandwichedbetween a pair of parallel substrates 11 and 12 includes a plurality ofliquid crystal molecules 14. The liquid crystal molecules 14 in thevicinity of boundaries with the substrates form a pretilt angle α, thedirection of which is such that the liquid crystal molecules 14 raise aforward end up (i.e., spaced from the substrate surface) in thedirections of uniaxial aligning treatment indicated by arrows A,respectively. I these figures, the uniaxial aligning treatment axisdirections A of the pair of substrates 11 and 12 are parallel to eachother and in an identical direction. Between the pair of substrates 11and 12, the liquid crystal molecules 14 form each smectic (molecular)layer 16 having a chevron structure where the smectic layer 16 is bentat a mid point between the substrates (hereinbelow, referred to as a“bending point”) and provides a layer inclination angle δ with respectto a normal to the substrates. These liquid crystal molecules 14 causeswitching between two stable states under electric field application andunder no electric field application, are stably present at a wallsurface of a virtual cone 15 having an apex angle 2 {circle over(H)}({circle over (H)}: a cone angle intrinsic to the liquid crystalmaterial used).

[0096] As shown in FIGS. 1A an 1B, the liquid crystal 13 between thesubstrates 11 and 12 can assume different two alignment states dependingon the pretilt directions of the liquid crystal molecules 14 in thevicinity of the substrate surface and the bending directions of thechevron structures of the smectic layers 16 between the substrates 11and 12. Herein, the alignment state shown in FIG. 1A is referred to as a“C1 alignment (state)” and the alignment state shown in FIG. 1B isreferred to a a “C2 alignment (state)”, respectively.

[0097] In both the C1 and C2 alignment states, all the liquid crystalmolecules 14 can assume two (optically) stable states within the cone 15in a thickness direction between the substrates of the device includingthe bending points under no electric field application by generallysatisfying a relationship of {circle over (H)}>δ, thus realizingbistable states.

[0098]FIGS. 2A and 2B are views for illustrating positions ofC-directors (projections of the liquid crystal molecules on a circularbase 17 of the virtual cone 15) in the C1 alignment shown in FIG. 1A andthe C2 alignment shown in FIG. 1B, respectively.

[0099] Referring to FIGS. 2A and 2B, each of the liquid crystalmolecules may assume bistable states 14 a and 14 b (projections 18 a and18 b) at any position between the substrates 11 and 12.

[0100] In the above (SSFLC-type) device wherein the liquid crystalassumes a bistability (bistable alignment states), a pair ofpolarizers-are disposed so that one of the polarizers is aligned withone of two average molecular axes (molecular positions) providing thetwo (optically) stable states, thus effecting a switching between thetwo stable states (bistable states) to allow a black (dark) and white(bright) display. In this case, the switching (between the two stablestates) is performed through formation of a domain of one of the twostable states from the other stable state, i.e., is accompanied withformation and extinction of domain walls.

[0101] In the case of effecting display based on such a switchingmechanism, the display is basically a two-value display providing ablack display state and a white display state. Accordingly, it isdifficult to effect a gradation (halftone) display between the black andwhite display state.

[0102] On the other hand, in the liquid crystal device used in thepresent invention, a liquid crystal material used is selected so that itdoes not exhibit the memory characteristic (bistability) as illustratedin FIGS. 1 and 2 and can continuously change its molecular positiondepending on a voltage applied thereto, in order to realize gradationaldisplay by the liquid crystal device using a liquid crystal materialassuming chiral smectic phase. For this reason, in the presentinvention, the liquid crystal material used may preferably be a liquidcrystal material exhibiting a phase transition series of Iso. (isotropicliquid phase)-Ch (cholesteric phase)-SmC* (chiral smectic C phase) or ofIso.-SmC* on temperature decrease.

[0103]FIG. 3A shows a course (process) of formation of smectic layerstructure of a liquid crystal material exhibiting a phase transitionseries on temperature decrease of at least Ch-SmA (smectic A phase)-SmC*and FIG. 3B shows a course of smectic layer structure formation of aliquid crystal material exhibiting at Ch-SmC* phase transition. serieson temperature decrease.

[0104] In these figures, an arrow R represents a direction of an averageuniaxial aligning treatment axis and an arrow LN represents a directionof a normal to smectic layer (layer normal direction). Further, theliquid crystal molecules 14 can effect switching along with the wallsurface of the virtual cone 15 at the time of voltage applicationthereto.

[0105] Herein, a direction of the “average uniaxial aligning treatmentaxis” means a direction of a uniaxial aligning treatment axis directionin the case where only one of the pair of substrates is subjected to auniaxial aligning treatment or a direction of two parallel uniaxialaligning treatment axes in the case where both of the pair of substratesare subjected to a uniaxial aligning treatment so that their uniaxialaligning treatment axes are parallel to each other and in the samedirection or opposite directions (parallel relationship or anti-parallelrelationship). Further, in the case where both of the substrates aresubjected to a uniaxial aligning treatment so that their uniaxialaligning treatment axes intersect each other at a crossing angle, the“average uniaxial aligning treatment axis” direction means a directionof a bisector of the uniaxial aligning treatment axes (a half of thecrossing angle).

[0106] Referring to FIG. 3A, in the case of the liquid crystal materialhaving the phase transition series including SmA (smectic A phase), theliquid crystal molecules 14 are oriented in SmA so that the (smectic)layer normal direction LN is aligned with the uniaxial aligningtreatment direction R, thus forming a smectic layer structure. In SmC*,the liquid crystal molecules 14 are tilted from the layer normaldirection LN and stabilized at a position in the vicinity of or slightlyinside an edge of the virtual cone 15.

[0107] On the other hand, in the case of the liquid crystal materialhaving the SmA-less phase transition series suitably used in the presentinvention, as shown in FIG. 3B, the liquid crystal molecules 14 areoriented in the phase transition from Ch to SmC* so that they are tiltedfrom the layer normal direction LN and also slightly tilted from theaverage uniaxial aligning treatment axis direction, thus forming asmectic layer structure.

[0108] In, the present invention, the liquid crystal material used iscontrolled so that the liquid crystal molecules 14 are stabilized at aposition (slightly) inside the edge of the virtual cone 15 in anoperation temperature range in SmC* to form a smectic layer structurehaving a chevron structure or an oblique bookshelf structure (wheresmectic layers are uniformly tilted from a direction of a normal to thesubstrates) providing a prescribed layer inclination angle.

[0109] In the case of a smectic layer structure having a completebookshelf structure, the liquid crystal molecules 14 an also bestabilized inside the virtual cone edge in some cases including a caseof a high pretilt angle or a case where liquid crystal molecules in abulk state are twisted due to a strong polar interaction at a boundarywith a substrate.

[0110] In the case where a liquid crystal material has a remarkableelectroclinic effect, the liquid crystal molecules are tilted outsidethe virtual cone edge under application of an electric field. Such aliquid crystal material having the electroclinic effect is alsoapplicable to the present invention since in the liquid crystal deviceused in the present invention, a deviation angle between the (liquidcrystal) molecular orientation direction and the layer normal directionunder electric field application is larger than a deviation angletherebetween under no electric field application. Specifically, when oneof polarizing axes of cross-nicol polarizers is aligned with the liquidcrystal molecular direction under no electric field application toprovide a darkest state, an optical axis of the liquid crystal materialused is deviated from the polarizing axis in either case of apositive-polarity voltage application and a negative-polarity voltageapplication, thus realizing birefringence.

[0111] Next, as an example of the liquid crystal material usable in thepresent invention, a liquid crystal material having a chevron or obliquebookshelf structure providing a layer inclination angle will bedescribed with reference to FIG. 4.

[0112]FIG. 4A shows a course of smectic layer structure formation ofliquid crystal molecules assuming a phase transition series free fromSmA similarly as in FIG. 3B.

[0113] Referring to FIG. 4A, the smectic layer structure is formed inthe course of phase transition from Ch to SmC* (particularly, at atemperature immediately below a phase transition temperature from Ch toSmC*) wherein the liquid crystal molecules 14 are oriented or aligned sothat they are tilted from the smectic layer normal direction LN.

[0114] In such a smectic layer structure formation, however the coneangle {circle over (H)} (half of an apex angle of the virtual cone 15)is different, e.g., between a higher-temperature state (T1) and alower-temperature state (T2) within SmC*-temperature range.

[0115] When a cone angle {circle over (H)} 1 in the higher-temperaturestate (T1) and a cone angle {circle over (H)}2 in the lower-temperaturestate (T2) of a liquid crystal material used is set so as to satisfy arelationship: {circle over (H)}1<{circle over (H)}2, in an ordinarycase, a layer spacing d1 in T1 and a layer spacing d2 in T2 hold arelationship: d1>d2.

[0116] Accordingly, if the liquid crystal material has a bookshelfstructure in T1, the liquid crystal material in T2 provides a layerinclination angle δ at least satisfying an equation: δ=cos⁻¹ (d2/d1). Asa result, in T2, the liquid crystal molecules of the liquid crystalmaterial form a chevron or oblique bookshelf structure. Of thesestructures, the chevron structure will be described.

[0117] Layer structures and positions of C-directors of a liquid crystalmaterial having a chevron structure are shown in FIGS. 4BA-4CB, whereinFIG. 4BA is a plan view showing a layer structure of liquid crystalmolecules 14 in C1 alignment and FIG. 4BB is a corresponding sectionalview showing the layer structure and positions of C-directions of theliquid crystal molecules 14 in C1 alignment and FIGS. 4CA and 4CB arethose in C2 alignment, respectively.

[0118] In these figures, the identical reference numerals and symbolshave the same meanings as in FIGS. 1 and 2.

[0119] As shown in these figures, the liquid crystal material having thechevron structure is controlled so that the liquid crystal molecules 14are stabilized inside the edge of the virtual cone 15 based on theabove-described relationships.

[0120] In all the cases shown in FIGS. 3A, 3B and 4A, the liquid crystalmolecules 14, e.g., as shown in FIGS. 1A to 2B may be considered to bestabilized in a bistable alignment state in the chevron (layer)structure, i.e., in two stable states where the liquid crystal moleculesare substantially parallel to the substrates 11 and 12. However, in thecases shown in FIGS. 3B and 4A, a constraint force becomes larger due tothe uniaxial aligning treatment. As a result, only one of these twostable states is stabilized, whereby a memory characteristic(bistability) of the liquid crystal material is lost.

[0121] Further, it may be assumed that the liquid crystal molecules 14form two smectic layer structures providing different layer normaldirections LN1 and LN2 as shown in FIG. 5 at the time of the phasetransition from Ch to SmC*, i.e., at a temperature immediately below thephase transition temperature from Ch to SmC*, as shown in FIGS. 3B and4A. In this instance, if the pair of substrates between which the(chiral smectic) liquid crystal material is disposed are subjected to acompletely symmetrical uniaxial aligning treatment, i.e., a uniaxialaligning treatment under identical conditions in terms of a treatingdirection, an alignment film material, etc., the two (different) smecticlayer structures shown in FIG. 5 are formed in an equivalent proportion.

[0122] In the liquid crystal device used in the present invention, thelayer structure formation of the liquid crystal material used isperformed so as to preferentially form only one of the above two smecticlayer structures, i.e., is performed so that a direction of deviation ofthe layer normal direction (LN1 or LN2, ordinarily LN1) from the averageuniaxial aligning treatment axis direction R is kept in a certaindirection, whereby the liquid crystal molecules 14 are stabilized insideone of two edges of the virtual cone 15 under no voltage application asshown in FIGS. 4BA-4CA, thus attaining a memory-less SmC* alignmentstate.

[0123] Then, an inversion behavior (to an electric field) of liquidcrystal molecules placed in such an alignment state that one of the twosmectic layer structures shown in FIG. 5 is preferentially formed in aliquid crystal device used in the present invention will be describedwith reference to FIGS. 6AA to 6D.

[0124] In these figures, the liquid crystal device employs a parallelrubbing cell (a pair of substrates subjected to a rubbing treatment (asa uniaxial aligning treatment) so that two rubbing directions areparallel and identical to each other) and the inversion behavior isexplained with respect to the liquid crystal molecules in C2 alignment.However, inversion behaviors in the cases of, e.g., C1 alignment,oblique bookshelf structure and anti-parallel rubbing cell can bediscussed similarly as in the case shown in FIGS. 6AA-6D as specificallydescribed below.

[0125] FIGS. 6AA, 6BA and 6CA are plan views showing molecular behaviors(I) under application of a positive-polarity electric field (E) (E>0),under no electric field application (E=0) and under application of anegative-polarity electric field (E<0), respectively. FIGS. 6AB, 6BB and6CB are sectional views showing molecular behaviors (II) correspondingto the molecular behaviors (I) shown in FIGS. 6AA, 6BA and 6CA,respectively, and also showing positions of corresponding C-directions(protections onto a circular base of a virtual cone), respectively.

[0126] In FIGS. 6AA, 6BA and 6CA showing the molecular behaviors (I),the liquid crystal molecules 14 are illustrated as an average molecularaxis thereof in a direction perpendicular to the substrates.

[0127] Under no electric field (voltage) application (E=0), s shown inFIG. 6BB, a C-director (projection) 18 on a circular base 17 (of avirtual cone 15) of a liquid crystal molecule 14 is somewhat deviatedfrom an average uniaxial aligning treatment axis direction R, andspontaneous polarizations 18′ of the liquid crystal molecules 14 aredirected substantially in the same direction between a pair ofsubstrates 11 and 12.

[0128] In this instance, when a cell (liquid crystal device) including apair of polarizers arranged in cross-nicol relationship is disposed sothat one of polarizing axes A and P (e.g., polarizing axis P) is alignedwith the liquid crystal molecular position (molecular axis) under novoltage application (FIGS. 6BA, 6BB and 6D), a resultant transmittedlight quantity passing through the liquid crystal layer is minimized toprovide a darkest state (black display state at a first emitting lightquantity).

[0129] When the liquid crystal molecules 14 placed in the alignmentstate shown in FIGS. 6BA and 6BB (E=0) are supplied with an electricfield (voltage) E, the liquid crystal molecules 14 ar tilted (switched)to positions depending on the polarity of the applied voltage E as shownin FIGS. 6AA, 6AB, 6CA and 6CB while having spontaneous polarizations 18(substantially uniformly directed to a direction of the applied voltageE. An angle of tilting based on the molecular position 14 under novoltage application (E=0) (hereinbelow, referred to as “tilting angle”)is increased depending on a magnitude (absolute value) of the appliedvoltage E. However, as apparent from FIGS. 6AA (E<0) and 6CA (E>0) whencompared with FIG. 6BA (E=0), the tilting angle (based on the molecularposition under E=0) in the case of application of the positive-polarity(one polarity) voltage (E>0, FIG. 6CA) is largely different from that inthe case of application of the negative-polarity (the other polarity)voltage (E<0, FIG. 6AA) even if absolute values of these(positive-polarity and negative-polarity) voltages are identical to eachother.

[0130] In the case of no voltage application (E=0) as shown in FIG. 6BA,the liquid crystal molecules 14 are (mono-)stabilized in a positionwhich is tilted from the (smectic) layer normal direction. In thisinstance, when sufficiently larger voltages of positive and negativepolarities each having an absolute value further larger than that o thevoltage E are applied to the liquid crystal molecules 14, respectively,the respective liquid crystal molecules 14 are further changed in theirpositions from those shown in FIGS. 6AA and 6CA, respectively, so thatthe directions of spontaneous polarization of the liquid crystalmolecules even in the vicinities of boundaries with the substrates 11and 12 are also aligned with the directions of electric fields E (E<0,E>0), respectively, similarly as in those of the liquid crystalmolecules 14 in a bulk state. As a result, almost all the liquid crystalmolecules 14 within the cell are present at the (virtual) cone angles,thus providing (two) maximum tilt states depending on the polarity ofthe applied voltage based on the molecular position under no voltageapplication (E=0, FIG. 6BA). As a result, the liquid crystal molecules14 are placed in a uniform alignment state substantially free fromtwisting thereof at two extreme molecular positions (on the virtual cone15) a bisector of which (corr. to the layer normal direction) is asymmetric axis thereof.

[0131] In the present invention, as described above, one of the maximumtilt states of the liquid crystal molecules 14 is controlled to bedifferent from the other maximum tilt state, whereby a tilting angle(based on the monostabilized molecular position under E=0) in onemaximum tilt state under the positive-polarity voltage application (E>0,FIG. 6CA) becomes larger than that in the other maximum tilt state underthe negative-polarity voltage application (E<0, FIG. 6AA).

[0132] In the case where Δnd (ΔN: refractive index anisotropy; d: cellthickness or thickness of liquid crystal layer) is set to be a valuecorresponding to ca. ½ of a wavelength of visible light, apositive-polarity voltage application (E>0) as shown in FIG. 6CAprovides a prescribed emitting light quantity from the liquid crystaldevice, i.e., a prescribed tilt state, with an increase in magnitude(absolute value) of the applied voltage E, thus providing a secondemitting light quantity most different from the first emitting lightquantity under no voltage application (E=0) (within a range of thepositive-polarity voltage application), i.e., a maximum transmittedlight quantity (in the case of E>0).

[0133] On the other hand, as shown in FIG. 6A, a negative-polarityvoltage application (E<0) provides an increased transmitted lightquantity passing through the liquid crystal device but a degree ofoptical response corresponding to the transmitted light quantity isconsiderably lower than the case of E>0 and provides a third emittinglight quantity most different from the first emitting light quantity(E=0) (within a range of the negative-polarity voltage application),i.e., a maximum transmitted light quantity (in the case of E<0) when theliquid crystal molecules are placed in a prescribed tilt state underapplication of a prescribed (negative-polarity) voltage (having anabsolute value identical to that of the positive voltage providing thesecond emitting light quantity).

[0134] However, a difference in maximum transmitted light quantitybetween the negative-polarity voltage application (E<0, FIG. 6AA) and novoltage application (E=0, FIG. 6BA) is smaller than a difference inmaximum transmitted light quantity between the positive-polarity voltageapplication (E>0, FIG. 6CA) and no voltage application (E=0, FIG. 6BA),thus attaining a maximum transmitting light quantity of the liquidcrystal device used in the present invention under the positive-polarityvoltage application.

[0135] In the case where a pair of polarizers having polarizing axes Aand P as shown in FIG. 6D is used, if a tilting angle (based on themonostabilized molecular position under E=0) of the liquid crystalmolecules 14 in the maximum tilt state under E>0 is at most 45 degrees,the liquid crystal molecules 14 located on the virtual cone 15 edge(i.e., in the maximum tilt state) provide the maximum transmitted lightquantity under E>0 (i.e., the second emitting light quantity). If thetilting angle of the liquid crystal molecules 14 is above 45 degrees,the liquid crystal molecules 14 located inside the virtual cone edgeprovide the maximum transmitted light quantity under E>0 (the secondemitting light quantity). On the other hand, in the case of applying thenegative-polarity voltage (E<0), the liquid crystal molecules 14 canprovide the maximum transmitted light quantity under E<0 (i.e., thethird emitting light quantity) in the maximum tilt state irrespective ofthe tilting angle thereof (based on the molecular position under E=0).

[0136] The liquid crystal device using the liquid crystal materialexhibiting the above-described switching (inversion) behavior of liquidcrystal molecules may, e.g., exhibit a voltage-transmittance (V-T)characteristic, particularly in the case where liquid crystal moleculesare placed in a maximum (largest) tilt state under positive-polarityvoltage application, as shown in FIG. 7.

[0137] Referring to FIG. 7, when a voltage (V) of a positive-polarity isapplied, a resultant transmittance (T) is continuously increased with amagnitude (absolute value) of the applied (positive-polarity) voltage(V) due to tilting of the liquid crystal molecules and shows a maximumtransmittance T1 under application of a voltage Vi or above. On theother hand, a negative-polarity voltage is applied, the transmittance(T) is somewhat continuously increased with an increasing magnitude ofthe applied (negative-polarity) voltage (V) but is saturated at T2,which is considerably lower than T1, under application of a voltage −V2or above (as an absolute value).

[0138] In the present invention, when the above-mentioned liquid crystaldevice allowing the switching behavior as shown in FIGS. 6AA to 6D andexhibiting the V-T characteristic as shown in FIG. 7 is used as anordinary liquid crystal panel of an active matrix type (equipped withTFTs) functioning as an optical shutter and is supplied with an AC(alternating current) driving waveform including a combination of one(positive)-polarity voltage application period (allowing the opticalresponse on the positive-polarity side shown in FIG. 7) and the other(negative)-polarity voltage application period (allowing the opticalresponse on the negative-polarity side shown in FIG. 7), it is possibleto attain an effect similar to that obtained in the above-describedmotion picture display scheme utilizing a time aperture rate of at most50%. Thus, it becomes possible to provide (liquid crystal) displayapparatus including the liquid crystal device improved in motion pictureimage qualities without using complicated peripheral circuits etc.

[0139] In this case, in order to further enhance the motion pictureimage qualities, it is preferred that a ratio of a tilting angle ofliquid crystal molecules (average molecular axis) in a maximum tiltstate (i.e., maximum tilting angle) under application of a voltage of afirst polarity (positive polarity in the case of FIG. 6CA) to a maximumtilting angle under application of a voltage of a second polarity(negative polarity in the case of FIG. 6AA) is set to be at least 5. Itis also preferred that a ratio of a maximum emitting light quantity(e.g., the transmittance T1 in FIG. 7) of liquid crystal molecules in aprescribed tilt state under the first (positive-)polarity voltageapplication to a maximum emitting light quantity (e.g., thetransmittance T2 in FIG. 7) of liquid crystal molecules in a maximumtilt state under the second (negative-)polarity voltage application isset to be at least 5.

[0140] Hereinbelow, an inversion (switching) mechanism of liquid crystalmolecules placed in some alignment states of a liquid crystal materialused in the liquid crystal device according to the present invention bycontrast with the SSFLC device.

[0141] When liquid crystal molecules of the SSFLC are placed in the C1and C2 alignment states shown in FIGS. 1A, 1B, 2A and 2C, the liquidcrystal molecules are required to cross or overcome an energy barrier ofa certain potential level in order to effect switching between bistablestates thereof in each of the C1 and C2 alignment states. The presenceof the energy barrier is the origin of bistability of a chiral smecticliquid crystal.

[0142] On the other hand, in the liquid crystal device used in thepresent invention, when liquid crystal molecules are, e.g., placed in analignment state as shown in FIG. 5, the liquid crystal molecules 14 areextremely stabilized at a position closer to a position at one ofbistable potentials of the SSFLC, thus resulting in only one stablestate. As a result in the present invention, an analog-like stable stateis present depending on a magnitude of an applied voltage, and theapplied provide one-to-one (corresponding) relationship, thus realizinginversion switching in a continuous manner without forming a domain(domain wall).

[0143] Examples of the energy barrier (potential level) are shown inFIGS. 8A, 8B, 9A and 9B.

[0144]FIGS. 8A and 8B show potential curves of the SSFLC in C1 alignmentand C2 alignment, respectively.

[0145] Referring to FIGS. 8A and 8B, A1 represents a potential in onestable state and A2 represents a potential in the other stable state.

[0146] As apparent from these figures, the SSFLC exhibits a potentialstate somewhat different in (potential) level between C1 alignment andC2 alignment.

[0147] In the case of C1 alignment of the SSFLC, an angle formed betweenaverage molecular axes in bistable states is larger than that in thecase of C2 alignment (of the SSFLC) (FIGS. 2A and 2B), thus resulting ina higher energy barrier.

[0148] On the other hand, FIGS. 9A and 9B show potential curves of aliquid crystal material in C1 alignment and C2 alignment, respectively,used in the liquid crystal device constituting the (liquid crystal)display apparatus of the present invention.

[0149] Referring to FIGS. 9A and 9B, B1 represents a potential under novoltage application (in the case of E=0 shown in FIGS. 6BA an 6BB), B2represents a potential (of liquid crystal molecules in a maximum tiltstate) under positive-polarity voltage application (in the case of E>0shown in FIGS. 6CA and 6CB), and B3 represents a potential (of liquidcrystal molecules in a maximum tilt state) under negative-polarityvoltage application (in the case of E<0 shown in FIGS. 6AA and 6AB).

[0150] As shown in these figures, the potential curves in C1 alignmentand C2 alignment are quite different from those of the SSFLC,respectively, thus resulting in a different driving characteristic.

[0151] Particularly, in C1 alignment providing higher energy barrier, asshown in FIG. 9A, even when the liquid crystal molecules are extremelystabilized at a position at the potential B1, a position at thepotential B2 can provide the liquid crystal molecules with a stablestate or metastable state (wherein the potential B2 is relatively higherbut is stable when compared with other positions). As a result, when thevoltage application for optical response of the liquid crystal moleculesin C1 alignment is performed, as analog-like stable state depending on amagnitude of the applied voltage is present and the applied voltage andthe resultant stable molecular position provide one-to-one relationship,thus realizing a continuous inversion switching with no domain wallformation. However, in some cases, a discontinuous alignment state isformed, i.e., a discontinuous inversion behavior with domain wallformation is effected, when the potential exceeds a certain level.

[0152] On the other hand, in C2 alignment as shown in FIG. 9B, theenergy barrier in the case of the SSFLC is lower. Accordingly, even whena position at the potential B1 is extremely stabilized, it is possibleto realize a continuous inversion switching with no domain wallformation to a position at the potential B2.

[0153] As is also understood from FIGS. 9A and 9B, a driving voltage isliable to become higher in the case of C1 alignment.

[0154] As described above, with respect to an alignment state of liquidcrystal molecules in the present invention, C2 alignment-may preferablybe adopted in a parallel rubbing cell in view of an analog-likegradational display performance and a lower driving voltage. Further, inthe case where the alignment state of liquid crystal molecules is onewherein C1 alignment and C2 alignment are co-present, a lower pretiltangle and/or an anti-parallel rubbing may desirably be adopted in orderto minimize fluctuations in analog-like gradational display performanceand driving voltage.

[0155] In the display apparatus of the present invention, theabove-described liquid crystal device exhibiting the inversion switchingbehavior such that the liquid crystal molecules 14 are (mono-)stabilizedinside one of the edges of the virtual cone 15 under no voltageapplication to lose a memory characteristic (bistability) in SmC* andare switched depending on the applied voltage value as shown in FIGS.6AA, 6AB, 6BA, 6BB, 6CA, 6CC, 9A and 9B and the V-T (optical response)characteristic as shown in FIG. 7 may, e.g., be prepared by using anappropriate liquid crystal material, controlling appropriately a celldesign and effecting such a treatment that an internal potential withina cell in the course f the phase transition from Ch to SmC* is localizedIn the present invention, as the liquid crystal material, a chiralsmectic liquid crystal material (or composition) may preferably be used.

[0156] Examples of the chiral smectic liquid crystal material mayinclude those of hydrocarbon-type containing a phenyl-pyrimidineskeleton, a biphenyl skeleton and/or a phenyl-cyclohexane esterskeleton. In the case where these materials have a layer spacing(d)-changing characteristic in a chiral smectic phase temperature rangesuch that a layer spacing (d_(tc)) at the upper limit temperature of thechiral smectic phase is a maximum value (d<d_(tc)) and a chevron (layer)structure within a cell, these materials may appropriately be blended toprepare a chiral smectic liquid crystal composition providing a layerinclination angle δ (degrees) satisfying: 3 (deg.)<δ<{circle over (H)}(δ: an inclination angle of smectic layer from a normal to substratewithin the cell; {circle over (H)}: the above-mentioned cone angle whichis half of the apex angle of the virtual cone).

[0157] It is also possible to use at least one species of liquid crystalmaterials of hydrocarbon-type containing a naphthalene skeleton orfluorine-containing liquid crystal materials. These materials maygenerally exhibit a substantially certain layer spacing (d) within achiral smectic phase temperature range and δ≦3 (deg.) within a cell. Inthis instance, these material may preferably be blended so as to preparea chiral smectic liquid crystal composition exhibiting a cone angle{circle over (H)}-changing characteristic such that a cone angle {circleover (H)} at a temperature immediately below the phase transitiontemperature from a higher-order phase to chiral smectic phase isgradually increased on temperature decrease within the chiral smecticphase temperature range.

[0158] In the present invention, a cone angle {circle over (H)} of theliquid crystal material in chiral smectic phase may ideally be at least22.5 deg. in order to further enhance a contrast between two statesproviding maximum and minimum light quantities based on switching ofliquid crystal materials (e.g., in order to further increase the maximumtransmittance Ti (E>0) in the V-T characteristic shown in FIG. 7). Onthe other hand, when the cone angle {circle over (H)} is very large, atilting angle from the monostabilized state under the otherpolarity-voltage application (i.e., a tilting angle toward the alignmentstate shown in FIG. 6AA (E<0)) also becomes larger. As a result, e.g.,the maximum transmittance T2 (E<0) in the V-T characteristic shown inFIG. 7 becomes larger, thus being liable to provide a time aperture rateof 100%. In view of this phenomenon, the cone angle may preferably bebelow 30 deg. Further, if the cone angle {circle over (H)} is largerchanged with temperature, a darkest state within a cell provided with apair of cross-nicol polarizers is liable not to be maintained. For thisreason, the cone angle {circle over (H)} may preferably be controlled sothat its value within a driving temperature range for the liquid crystaldevice is fluctuated within ±3 deg.

[0159] In the case where the liquid crystal material has a layerspacing-changing characteristic such that a layer spacing is decreasedby tilting of liquid crystal molecules from a (smectic) layer normaldirection similarly as in an ordinary liquid crystal material assumingSmC* (i.e., in the case of a liquid crystal material providing anincreasing cone angle {circle over (H)} on temperature decrease), afactor of decreasing the layer spacing becomes larger. However, when theliquid crystal material used is, e.g., a fluorine-containing liquidcrystal material which per se spontaneously exhibiting a bookshelf(layer) structure, the change in layer spacing can be made very smallbased on a property intrinsic to the fluorine-containing liquid crystalmaterial such that the layer spacing measured in a bulk state becomeslarger on temperature decrease. This may be considered to be the reasonwhy the fluorine-containing liquid crystal material is not readilyformed. In this instance, liquid crystal molecules at a boundary with asubstrate ar aligned with a rubbing (uniaxial aligning treatment)direction due to a uniaxial aligning control force and bulk liquidcrystal molecules are oriented in a direction deviated from the rubbingdirection depending on the temperature characteristic of the cone angle{circle over (H)} in some cases. At that time, if an electric field isapplied to the liquid crystal material, the boundary liquid crystalmolecules are also oriented in a direction deviated from the rubbingdirection similarly as in the bulk liquid crystal molecules.

[0160] Incidentally, in order to provide an internal potentiallocalization within the liquid crystal device for preferentially formingone of two (smectic) layer structures as shown in FIG. 5, i.e., formaking constant a deviation direction of a smectic layer normal from anaverage uniaxial aligning treatment axis, for example, the followingmethods (1)-(4) may be adopted.

[0161] (1) During a phase transition from Ch to SmC* or from Iso. toSmC*, a DC (direct current) voltage of a positive or negative polarityis applied between a pair of substrates.

[0162] (2) A pair of substrates is provided with alignment filmsdifferent in material, respectively.

[0163] (3) A pair of substrates each provided with an alignment film issubjected to different treating methods in terms of, e.g., film-formingconditions, rubbing strength, and UV irradiation conditions.

[0164] (4) A pair of substrates each provided with an alignment film isfurther provided with a layer underlying the alignment film and theunderlying layer is changed in material or thickness for each substrate.

[0165] In the above method (1), in order to avoid an occurrence of shortcircuit between the pair of substrates constituting the liquid crystaldevice due to a DC voltage application for a long period of time, the DCvoltage application time may preferably be as short as possible if it issufficient to provide a uniform layer formation direction. Specifically,the applied DC voltage may preferably be 100 mV to 10 V.

[0166] Ions (impurities) within the above-mentioned liquid crystalmaterials and the alignment films as used in the above methods (2), (3)and (4) may desirably be as little as possible so as not to adverselyaffect TFT-driving scheme.

[0167] In order to monostabilize liquid crystal molecules (averagemolecular axis) under no voltage application within the liquid crystaldevice used in the present invention, a uniaxial aligning control forceis required to be large.

[0168] With respect to this aligning control force, an evaluation methodusing a cholesteric liquid crystal has been proposed by Uchida et al.(“Liquid Crystals”, vol. 5, p. 1127 (1989)). More specifically,according to this method, it is possible to evaluate the aligningcontrol force by determining an “effective twisting angle” based on atorque balance between a helical pitch in cholesteric phase and thealigning control force.

[0169] In the present invention, based on this method, the uniaxialaligning control force may be evaluated as follow.

[0170] In the case where the liquid crystal material used in the liquidcrystal device has cholesteric phase, when there is no aligning controlforce, the following relationship is fulfilled:

dg/p=φ/2π,

[0171] wherein dg represents a cell thickness, p represents acholesteric (helical) pitch and φ represents a twisting angle within acell.

[0172] On the other hand, in the case where a pair of substrates issubjected to uniaxial aligning treatment so that their uniaxial aligningtreatment axes are parallel to each other to provide an infinite(extremely larger) aligning control force, the resultant twisting angleφ becomes zero. The twisting angle φ may be readily determined bymeasuring optical rotation through a polarizing microscope similarly asin the above Uchida et al. method. More specifically, with the cell, thecholesteric liquid crystal has a virtual helical pitch p* (=2π×dg/φ)larger than the original helical pitch p due to the aligning controlforce. In other words, the aligning control force may be defined as zerowhen p*=p and infinite when p* is infinite.

[0173] In the present invention, it is preferred to at least satisfyp*≧2×p, more preferably p*≧10×p in order to ensure themonostabilization.

[0174] In view of the above circumferences, in the present invention, itis preferred to appropriately set uniaxial aligning treatment (e.g.,rubbing) conditions, aligning film thickness, alignment film material,curing conditions for the aligning film, etc. according to theabove-mentioned methods (2)-(4).

[0175] In the present invention, when a V-T characteristic is determinedunder application of a triangular wave, a hysteresis phenomenon isobserved in some cases.

[0176] However, when the liquid crystal device is driven by applying anAC waveform as in an actual TFT-type liquid crystal device, thehysteresis phenomenon is of substantially no problem since a continuousoptical modulation form a white state to a halftone state as in the caseof the triangular wave application is not effected. More specifically,in the case of the AC waveform application, an optical modulation isperformed while always effecting inversion between white and black(alignment) states depending on a polarity of an applied voltage. Forexample, when an optical modulation from a white state to a halftonestate, the white to halftone optical modulation is performed from thewhite state to the halftone state via, the white to halftone opticalmodulation is performed from the white state to the halftone state via ablack state, so that the AC waveform application allows such a drivingoperation that a display state is written after always resetting in ablack state on the side of one of two polarities. As a result, anadverse affect of a previous state (display history) can be considerablysuppressed.

[0177] Hereinbelow, an embodiment of the liquid crystal device used inthe present invention will be described with reference to FIG. 10.

[0178]FIG. 10 shows a schematic sectional view of a liquid crystaldevice 80 constituting a (liquid crystal) display apparatus according tothe present invention.

[0179] The liquid crystal device 80 includes a pair of substrates 81 aand 81 b; electrodes 82 a and 82 b disposed on the substrates 81 a and81 b, respectively; insulating films 83 a and 83 b disposed on theelectrodes 82 a and 82 b, respectively; alignment control films 84 a and84 b disposed on the insulating films 83 a and 83 b, respectively; aliquid crystal 85 disposed between the alignment control films 84 a and84 b; a spacer 86 disposed together with the liquid crystal 85 betweenthe alignment control films 84 a and 84 b; and a pair of polarizers (notshown) sandwiching the pair of substrates 81 a and 81 b with polarizingaxes arranged perpendicular to each other (cross-nicol relationship).

[0180] The liquid crystal 85 may preferably assume chiral smectic phase.

[0181] Each of the substrates 81 a and 81 b comprises a transparentmaterial, such as glass or plastics, and is coated with, e.g., aplurality of stripe electrodes 82 a (82 b) of In₂O₃ or ITO (indium tinoxide) for applying a voltage to the liquid crystal 85. These electrodes82 b and 82 b intersect each other to form a matrix electrode structure,thus providing a simple matrix-type liquid crystal device. As amodification of the electrode structure, one of the substrates 81 a and81 b may be provided with a matrix electrode structure whereindot-shaped transparent electrodes are disposed in a matrix form and eachof the transparent electrodes is connected to a switching element, suchas a TFT (thin film transistor) or MIM (metal-insulator-metal), and theother substrate may be provided with a counter (common) electrode on itsentire surface or in an prescribed pattern, thus constituting an activematrix-type liquid crystal device.

[0182] On the electrodes 82 a and 82 b, the insulating films 83 a and 83b, e.g., of SiO₂, TiO₂ or Ta₂O₅ having a function of preventing anoccurrence of short circuit may be disposed, respectively, as desired.

[0183] On the insulating films 83 a and 83 b, the alignment controlfilms 84 a and 84 b are disposed so as to control the alignment state ofthe liquid crystal 85 contacting the alignment control films 84 a and 84b. At least one of (preferably both of) the alignment control films 84 aand 84 b is subjected to a uniaxial aligning treatment (e.g., rubbing).Such an alignment control film 84 a (84 b) may be prepared by forming afilm Of an organic material (such as polyimide, polyimideamide,polyamide or polyvinyl alcohol through wet coating with a solvent,followed by drying and rubbing in a prescribed direction or by forming adeposited film of an inorganic material through an oblique vapordeposition such that an oxide (e.g., SiO) or a nitride isvapor-deposited onto a substrate in an oblique direction with aprescribed angle to the substrate.

[0184] The alignment control films 84 a and 84 b may appropriately becontrolled to provide liquid crystal molecules of the liquid crystal 85with a prescribed pretilt angle a (an angle formed between the liquidcrystal molecule and the alignment control film surface at theboundaries with the alignment control films) by changing the materialand treating conditions (of the uniaxial aligning treatment).

[0185] In the case where both of the alignment control films 84 a and 84b are subjected to the uniaxial aligning treatment (rubbing), therespective uniaxial aligning treatment (rubbing) directions mayappropriately be set in a parallel relationship, an anti-parallelrelationship or a crossed relationship providing a crossing angle of atmost 45 degrees, depending on the liquid crystal material used.

[0186] The substrates 81 a and 81 b are disposed opposite to each othervia the spacer 86 comprising e.g., silica beads for determining adistance (i.e., cell gap) therebetween, preferably in the range of0.3-10 μm, in order to provide a uniform uniaxial aligning performanceand such an alignment state that an average molecular axis of the liquidcrystal molecules under no electric field application is substantiallyaligned with an average uniaxial aligning treatment axis (a bisector oftwo uniaxial aligning treatment axes) although the cell gap varies itsoptimum range and its upper limit depending on the liquid crystalmaterial used.

[0187] In addition to the spacer 86, it is also possible to disperseadhesive particles of a resin (e.g., epoxy resin) (not shown) betweenthe substrates 81 a and 81 b in order to improve adhesivenesstherebetween and an impact (shock) resistance of the liquid crystalhaving chiral smectic C phase (SmC*).

[0188] A liquid crystal device 80 having the above cell structure and aspecific alignment state as shown in FIGS. 6AA to 6CB can be prepared byusing a liquid crystal material 85 exhibiting a chiral smectic phase,while adjusting the composition thereof, and further by appropriateadjustment of the liquid crystal material treatment, the devicestructure including a material, and a treatment condition for alignmentcontrol films 84 a and 84 b. More specifically, the alignment state ofFIGS. 6AA to 6CB is realized by a liquid crystal device wherein theliquid crystal molecules are aligned to provide an average molecularaxis to be mono-stabilized in the absence of an electric field appliedthereto and, under application of voltages of one polarity (a firstpolarity), are realigned to provide a tilting angle which variescontinuously from the average molecular axis of the monostabilizedposition depending on the magnitude of the applied voltage. On the otherhand, under application of voltages of the other polarity (i.e., asecond polarity opposite to the first polarity), the liquid crystalmolecules are tilted from the average molecular axis under no electricfield depending on the magnitude of the applied voltages, but themaximum tilting angle obtained under application of the second polarityvoltages is substantially smaller than the maximum tilting angle formedunder application of the first polarity voltages. The liquid crystalmaterial showing a chiral smectic phase may preferably exhibit a phasetransition series on temperature decrease of Iso. (isotropic phase)-Ch(cholesteric phase)-SmC* (chiral smectic C phase) or Iso. phase-SmC* andbe placed in a non-memory state in the SmC* by using the above-mentionedmethods (1)-(4).

[0189] The liquid crystal material 85 showing chiral smectic phase maypreferably have a helical pitch which is at least twice a cell gap in abulk state thereof.

[0190] The liquid crystal material 85 showing chiral smectic phase maypreferably be a composition prepared by appropriately blending aplurality of liquid crystal materials exhibiting, e.g., theabove-described characteristics (in terms of a cone angle {circle over(H)}, a (smectic) layer spacing d and a layer inclination angle δ)selected from hydrocarbon-type liquid crystal materials containing abiphenyl, phenyl-cyclohexane ester or phenyl-pyrimidine skeleton,naphthalene-type liquid crystal materials and fluorine-containing liquidcrystal materials.

[0191] When the liquid crystal device 80 as described above has such acell structure that at least one of the substrates 81 a and 81 b isprovided with a polarizer and the cell is disposed to provide a darkeststate under no voltage application, a tilting angle of liquid crystalmolecules (of the liquid crystal material 85) varies continuously undervoltage application as described above to provide a V-T characteristicas shown in FIG. 7. As a result, a resultant transmitted light quantityof the device (emitting light quantity from the device) can becontrolled in an analog-like manner with a change in applied voltage.

[0192] The liquid crystal device used in the present invention may beformed in a color liquid crystal device by providing one of thesubstrates 81 a and 81 b with a color filter comprising color filtersegments of at least red (R), green (G) and blue (B).

[0193] In the present invention, the liquid crystal device may beapplicable to various liquid crystal devices including: a liquid crystaldevice of a transmission-type herein a pair of transparent substrates 81a and 81 b is sandwiched between a pair of polarizers to opticallymodulate incident light (e.g., from an eternal light source) through oneof the substrate 81 a and 81 b to be passed through the other substrate,and a liquid crystal device of a reflection-type wherein at least one ofa pair of substrates 81 a and 81 b is provided with a polarizer tooptically modulate incident light and reflected light and pass the lightthrough the substrate on the light incident side. The reflection-typeliquid crystal device may, e.g., be prepared by providing a reflectionplate to either one of the substrates 81 a and 81 b or forming of areflective material one of the substrates or a reflecting memberprovided thereto.

[0194] In the present invention, by using the above-mentioned liquidcrystal device in combination with a drive circuit for supplyinggradation signals to the liquid crystal device, it is possible toprovide a liquid crystal display apparatus capable of effecting agradational display based on the above-mentioned alignment and V-Tcharacteristics such that under voltage application, a resultant tiltingangle varies continuously from the monostabilized position of theaverage molecular axis (of liquid crystal molecules) and a correspondingemitting light quantity continuously changes.

[0195] For example, it is possible to use, as one of the pair ofsubstrates, an active matrix substrate provided with a plurality ofswitching elements (e.g., TFT (thin film transistor) or MIM(metal-insulator-metal)) in combination with a drive circuit (drivemeans), thus effecting an active matrix drive based on amplitudemodulation to allow a gradational display in an analog-like gradationmanner.

[0196] Hereinbelow, an embodiment of a liquid crystal display apparatusof the present invention including a liquid crystal device provided withsuch an active matrix substrate will be explained with reference toFIGS. 11-13.

[0197]FIG. 11 shows a schematic plan view of such a display apparatusincluding a liquid crystal device and a drive circuit (means) andprincipally illustrates a structure on the active matrix substrate side.

[0198] Referring to FIG. 11, a liquid crystal device (panel) 90 includesa structure such that gate lines (G1, G2, G3, G4, G5, . . . )corresponding to scanning lines connected to a scanning signal driver 91(drive means) and source lines (S1, S2, S3, S4, S5, . . . )corresponding to data signal lines connected to a data signal driver 92(drive means) are disposed to intersect each other at right angles in anelectrically isolated state, thus forming a plurality of pixels (5×5 inFIG. 11) each at intersection thereof. Each pixel is provided with athin film transistor (TFT) 94 as a switching element and a pixelelectrode 95 (as an effective drive region). The switching element maybe a metal-insulator-metal (MIM) element. The gate lines (G1, G2, . . .) are connected with gate electrodes (not shown) of the TFT 94,respectively, and the source lines (S1, S2, . . . ) are connected withsource electrodes (not shown) of the TFT 94, respectively. The pixelelectrodes 95 are connected with drain electrodes (not shown) of the TFT94, respectively.

[0199] A gate voltage is supplied to the gate lines (G1, G2, . . . )from the scanning signal driver 91 by effecting scanning selection in,e.g., a line-sequential manner. In synchronism with this scanningselection on the gate lines, the source lines (S1, S2, . . . ) aresupplied with a data signal voltage depending on writing data for eachpixel from the data signal driver 92. The thus-supplied gate and datasignal voltages are applied to each pixel electrode 95 via the TFT 94.

[0200]FIG. 12 shows a sectional structure of each pixel portion (corr.to 1 bit) in the panel structure shown in FIG. 11.

[0201] Referring to FIG. 12, a layer of a liquid crystal material 49having a spontaneous polarization are sandwiched between an activematrix substrate or plate 20 provided with a TFT 94 and a pixelelectrode 95 and an opposing substrate or plate 40 provided with acommon electrode 42, thus providing a liquid crystal capacitor (C1 c) 31of the liquid crystal layer 49.

[0202] In this embodiment, the active matrix substrate 20 includes anamorphous silicon (a-Si) TFT as the TFT 94. The TFT may be of a polycrystalline-Si type, i.e., (p-Si) TFT.

[0203] The TFT 94 is formed on a substrate 21 of, e.g., glass andincludes: a gate electrode 22 connected with the gate lines (G1, G2, . .. shown in FIG. 11); an insulating film (gate insulating film) 23 of,e.g., silicon nitride (SiNx) formed on the gate electrode 22; an a-Silayer 24 formed on the insulating film 23; n⁺ a-Si layers 25 and 26formed on the a-Si layer 24 and spaced apart from each other; a sourceelectrode 27 formed on the n⁺ a-Si layer 25; a drain electrode 28 formedon the n⁺ a-Si layer 26 and spaced apart from the source electrode 27; achannel protective film 29 partially covering the a-Si layer 24 and thesource and drain electrodes 27 and 28. The source electrode 27 isconnected with the source lines (S1, S2, . . . shown in FIG. 11) and thedrain electrode 28 is connected with the pixel electrode 95 (FIG. 11) ofa transparent conductor film (e.g., ITO film). The TFT 94 is placed inan “ON” state by applying a gate pulse to the gate electrode 22 during ascanning selection period of the corresponding gate line.

[0204] Further, on the active matrix substrate 20, a structureconstituting a holding or supplementary capacitor (Cs) 32 is formed bythe pixel electrode 95, a holding capacitor electrode 30 disposed on thesubstrate 21, and a portion of the insulating film 23 sandwichedtherebetween. The structure (holding capacitor) (Cs) 32 is disposed inparallel with the liquid crystal capacitor (C1 c) 31. In the case wherethe holding capacitor electrode 30 has a large area, a resultantaperture or opening rate is decreased. In such a case, the holdingcapacitor electrode 30 is formed of a transparent conductor film (e.g.,ITO film).

[0205] On the TFT 94 and the pixel electrode 95 of the active matrixsubstrate 20, an alignment film 43 a for controlling an alignment stateof the liquid crystal 49. The alignment film 43 a is subjected to auniaxial aligning treatment (e.g., rubbing).

[0206] On the other hand, the opposing substrate 40 includes a substrate(e.g., glass substrate) 41; a common electrode 42 having a uniformthickness disposed on the entire substrate 41; and an alignment film 43b having a uniform thickness, disposed on the common electrode 42, forcontrolling an alignment state of the liquid crystal 49.

[0207] The above panel (cell) structure (liquid crystal device)including a plurality of the pixels each having the structure shown inFIG. 12 is sandwiched between a pair of polarizers (not shown) withpolarizing axes intersecting each other at right angles.

[0208] The liquid crystal material constituting the liquid crystal layer49 may preferably be a chiral smectic liquid crystal (composition) whichhas a spontaneous polarization and exhibits the above-mentionedalignment state (or switching behavior) shown in FIGS. 6AA-6D and V-T(optical response) characteristic shown in FIG. 7.

[0209] Next, an example of an ordinary active matrix driving methodaccording to the present invention utilizing the liquid crystal deviceusing the active matrix substrate (plate) and a chiral smectic liquidcrystal having the characteristics as described above will be describedwith reference to FIGS. 13 and 14 in combination with FIGS. 11 and 12.

[0210]FIG. 13 shows an example of an equivalent circuit for each pixelportion of such a liquid crystal device shown in FIG. 12.

[0211] In the active matrix driving method according to the presentinvention described below, the liquid crystal material used for theliquid crystal layer 49 comprises a chiral smectic liquid crystal(composition) providing a V-T characteristic as shown in FIG. 7 and, asshown in FIG. 14, one frame period F0 for displaying a prescribedinformation (e.g., a full-color image) is divided into a plurality offield periods F1, F2, . . . , each for a prescribed image (e.g., any oneof color images of R, G and B), and each of the field periods (e.g., thefield period F1) is further divided into a plurality of sub-fieldperiods (1F and 2F in this embodiment).

[0212] In each of the sub-field periods 1F and 2F, a prescribed emittingliquid quantity depending on a prescribed image information for eachsub-field period is obtained. Further, in each field period (e.g., F1),an average of the emitting light quantities in the sub-field periods 1Fand 2F is obtained to provide a prescribed image (e.g., red image). As aresult, in one frame period F0, a desired display information (e.g., afull-color image) can be provided based on plural images displayed inthe plurality of field periods F1, F2, . . .

[0213]FIG. 14 shows at (a) a voltage waveform applied to one gate line(e.g., G1 shown in FIG. 11) (as a scanning line) connected with eachpixel.

[0214] In the liquid crystal device driven by the active matrix drivingmethod, the gate lines G1, G2, . . . shown in FIG. 20 are selected in aline-sequential manner in each of the sub-field periods 1F and 2F. Atthis time, each gate electrode 22 connected with a corresponding gateline is supplied with a prescribed gate voltage Vg in a selection periodTon of each sub-field period (e.g., 1F), thus placing the TFT 94 in an“ON” state. In a non-selection period Toff (of, e.g., the sub-fieldperiod 1F) corresponding to a period in which other gate lines areselected, the gate electrode 22 is not supplied with the gate voltageVg, thus placing the TFT 94 in an “OFF” state (high-resistance state).In every non-selection period Toff, a prescribed and same gate line isselected and a corresponding gate electrode 22 is supplied with the gatevoltage Vg.

[0215]FIG. 14 shows at (b) a voltage waveform applied to one source line(e.g., S1 shown in FIG. 11) (as a data signal line) connected to thepixel concerned.

[0216] When the gate electrode 22 is supplied with the gate voltage Vgin the selection period Ton of each sub-field period 1F or 2F as shownat (a) of FIG. 14, in synchronism with this voltage application, aprescribed source voltage (data signal voltage) Vs having a prescribedpotential providing a writing data (pulse) to the pixel concerned isapplied to a source electrode 27 through the source line connected withthe pixel based on a potential Vc of a common electrode 42 as areference potential.

[0217] More specifically, in the first sub-field period 1F constitutingthe first field period F1, a positive-polarity source voltage Vs havinga potential Vx (═V) (based on a reference potential Vc) providing adesired optical state or display data (transmittance) based on the V-Tcharacteristic as shown in FIG. 7 is applied to the source electrode 27concerned.

[0218] At this time, the TFT 94 is in an “ON” state, whereby thepositive-polarity source voltage Vx applied to the source electrode 27is supplied to a pixel electrode 95 via a drain electrode 28, thuscharging a liquid crystal capacitor (C1 c) 31 and a holding capacitor(Cs) 32. As a result, the potential of the pixel electrode 95 becomes alevel equal to that of the positive-polarity source (data signal)voltage Vx.

[0219] Then, in a subsequent non-selection period Toff, for the gateline on the pixel concerned, the TFT 94 is in an “OFF” (high-resistance)state. At this time (in T_(off) of 1F), in the liquid crystal cell, theliquid crystal capacitor (C1 c) 31 and the holding capacitor (Cs) 32retain the electric charges therein, respectively, charged in theselection period T_(on) to keep the (positive-polarity) voltage Vx. As aresult, the liquid crystal layer 49 of the pixel concerned is suppliedwith the voltage Vx through the first field period 1F to provide thereata desired optical state (transmitted light quantity) by depending on thevoltage Vx.

[0220] Thereafter, in the second (subsequent) sub-field period 2Fconstituting the first field period F1, a negative-polarity sourcevoltage Vs (=−Vx) having an identical potential (absolute value) to buta polarity opposite to the source voltage Vs (=Vx) applied in the firstsub-field period 1F is applied to the source electrode 27 concerned.

[0221]FIG. 14 shows at (c) a waveform of a pixel voltage Vpix actuallyheld by the liquid crystal capacitor (C1 c) 31 and the holding capacitor(Cs) 32 of the pixel concerned and applied to the liquid crystal layer49, and FIG. 14 shows at (d) an example of an actual optical response(in the case of a liquid crystal device of a transmission-type) at thepixel concerned.

[0222] As shown at (c) of FIG. 14, an applied voltage through twosub-field periods 1F and 2F comprises the positive-polarity voltage Vxin the first sub-field period 1F and the negative-polarity voltage −Vx(having the same amplitude (absolute value) as Vx). In the firstsub-field period 1F, as shown at (d) of FIG. 14, a gradational displaystate is obtained depending on Vx, and in the second sub-field period2F, depending on −Vx, another gradational display state is obtained. Forexample, when these voltage Vx and −Vx are set to voltages V1 and −V1,respectively, as shown in FIG. 7, a higher luminance or transmittedlight quantity Tx (transmittance Ti in FIG. 7) is obtained in the firstsub-field period 1F. On the other hand, in the second sub-field period2F, a lower luminance or transmitted liquid quantity 1F. On the otherhand, in the second sub-field period 2F, a lower luminance ortransmitted light quantity Ty (transmittance T2 in FIG. 7) which iscloser to zero but a non-zero value.

[0223] At this time, the TFT 94 is in an “ON” state, whereby thenegative-polarity source voltage −Vx applied to the source electrode 27is supplied to a pixel electrode 95, thus charging a liquid crystalcapacitor (C1 c) 31 and a holding capacitor (Cs) 32. As a result, thepotential of the pixel electrode 95 becomes a level equal to that of thenegative-polarity source (data signal) voltage −Vx.

[0224] Then, in a subsequent non-selection period Toff, for the gateline on the pixel concerned, the TFT 94 is in an “OFF” (high-resistance)state. At this time (in T_(off) of 2F), in the liquid crystal cell, theliquid crystal capacitor (C1 c) 31 and the holding capacitor (Cs) 32retain the electric charges therein, respectively, charged in theselection period Ton to keep the (negative-polarity) voltage Vx. As aresult, the liquid crystal layer 49 of the pixel concerned is suppliedwith the voltage Vx through the second field period 2F to providethereat a desired optical state (transmitted light quantity) bydepending on the voltage Vx.

[0225] As described above, by using the chiral smectic liquid crystal asthe liquid crystal material providing the V-T characteristic as shown inFIG. 7 in the active matrix driving method, it becomes possible toeffect a good gradational display based on a high-speed responsivenessof the chiral smectic liquid crystal. In addition, a gradational displayof a prescribed level at each pixel is continuously performed bydividing one field pixel (e.g., F1) into a first sub-field pixel 1Fproviding a higher transmitted light quantity and a second sub-fieldperiod 2F providing a lower transmitted light quantity, thus resultingin a time aperture rate of at most 50% to improve a human-sensiblehigh-speed responsiveness with respect to motion picture display.Further, in the second sub-field period 2F providing the lowertransmitted light quantity, the resultant transmitted light quantity isnot zero due to a slight switching (inversion) performance of liquidcrystal molecules, thus ensuring a certain human-sensible luminancethrough the entire field period (and also through the entire frameperiod).

[0226] In the present invention, the above-described higher luminancedisplay at the transmitted light quantity Tx (performed in the firstsub-field period 1F in the above embodiment) may be performed in thesecond sub-field period 2F and the lower luminances display at thetransmitted light quantity Ty (performed in the second sub-field period2F may be performed in the first sub-field period 1F. Thus, the order ofhigher and lower luminance displays may appropriately be changed to anyorder as desired.

[0227] In the above embodiment, the polarity of the voltage (Vx or −Vx)is changed alternately for every sub-field period (1F or 2F) (i.e.,polarity-inversion for each sub-field period), whereby the voltageactually applied to the liquid crystal layer 49 is continuously changedin an alternating manner to suppress a deterioration of the liquidcrystal material used even in a continuous display operation for a longperiod.

[0228] As described above, in the above active matrix driving method, ineach field period (e.g., F1) consisting of two sub-field periods 1F and2F, a resultant transmitted light quantity corresponds to an average ofTx and Ty. Accordingly, in order to obtain a further higher transmittedlight quantity in each field period, it is preferred to apply a source(data signal) voltage Vs providing a transmitted light quantity higherthan Tx in the first sub-field substrate 1F by a prescribed level basedon the V-T characteristic as shown in FIG. 7.

Second Embodiment

[0229]FIG. 15 shows an example of a liquid crystal display apparatus 100of the present invention according to this embodiment.

[0230] Referring to FIG. 15, the liquid crystal display apparatus 100incudes a color light source 101 emitting a plurality of color lightsand a display device 80 effecting switching of the color lights insynchronism with emission of the respective color lights.

[0231] The display device 80 in this embodiment is a liquid crystaldevice having a cell structure as shown in FIG. 10.

[0232] As shown in FIG. 10, the liquid crystal device 80 has such a cellstructure that a liquid crystal 85 is disposed between a pair ofsubstrates 81 a and 81 b each provided with a plurality of electrodes 82a or 82 b so as to form a plurality of pixels each at an intersection ofthe electrodes 82 a and 82 b.

[0233] The liquid crystal device 80 in this embodiment may be of asimple matrix-type (FIG. 10) or active matrix-type (FIGS. 11 and 12) andalso may be of a transmission-type or reflection-type, similarly as inthe above-mentioned First Embodiment.

[0234] The liquid crystal device 80 may be prepared in the same manneras in First Embodiment described above.

[0235] The liquid crystal 85 (liquid crystal material) may be one havinga spontaneous polarization, e.g., a chiral smectic liquid crystal(composition). The liquid crystal 85 may preferably assume an alignment(or switching) characteristic as shown in FIGS. 6AA-6D and an optical(V-T) characteristic as shown in FIG. 7.

[0236] More specifically, the liquid crystal 85 used in the liquidcrystal device 80 may preferably have alignment and V-T characteristicssuch that an average molecular axis of liquid crystal molecules ismonostabilized under no voltage application and, under application ofvoltages of one polarity is tilted from the monostabilized position inone direction and, under application position in one direction and,under application of voltages of the other polarity (opposite to theabove one polarity), is tilted from the monostabilized position in theother direction (opposite to the above one direction).

[0237] When the voltages of one polarity and the other polarity areapplied to the (chiral smectic) liquid crystal 85, a tilting angle basedon the monostabilized position of the average molecular axis of liquidcrystal molecules varies continuously depending on the magnitude of thevoltage applied to the liquid crystal 85. As a result a light quantityemitted from the liquid crystal device 80 also changes its valuedepending on the magnitude of the applied voltage, thus allowing agradational display in combination with a drive circuit (means) forsupplying gradation signals to the liquid crystal device 80 connectedthereto.

[0238] In this instance, a maximum value of the tilting angle (maximumtilting angle) in the case of one polarity-voltage application maypreferably be different from that in the case of the otherpolarity-voltage application. As a result, a corresponding maximumemitting light quantity (first light quantity) in the case ofpolarity-voltage application is also different from that (secondlight-quantity) in the case of the other polarity-voltage application.

[0239] The maximum tilting angle under one polarity-voltage applicationmay preferably be larger than, more preferably at least five times aslarge as, that under the other polarity-voltage application. As aresult, a corresponding first light quantity is larger than, preferablyat least five times as large as, a corresponding second light quantity.

[0240] Further, it is also preferred to provide a tilting angle ofsubstantially zero in the case of the other polarity-voltageapplication.

[0241] It is also possible to provide an emitting light quantity (thirdlight quantity) in the absence of voltage application by appropriatelyarranging a pair of polarizers.

[0242] The chiral smectic liquid crystal 85 exhibiting theabove-mentioned characteristics may be prepared by using a liquidcrystal material which assumes a phase transition series of Iso.-Ch-SmC*or Iso.-SmC* on temperature decrease and has a smectic layer normaldirection substantially aligned with one direction and loses its memorycharacteristic in SmC*.

[0243] In order to realize a non-memory state of the liquid crystal 85,it is possible to adopt the following methods (i) to (iv):

[0244] (i) a method wherein the liquid crystal 85 disposed between apair of substrates is supplied with a DC voltage of a positive polarityor negative polarity,

[0245] (ii) a method wherein oppositely disposed two alignment controlfilms contacting the liquid crystal 85 are formed of differentmaterials,

[0246] (iii) a method wherein oppositely disposed two alignment controlfilms contacting the liquid crystal 85 are subjected to differenttreatments in terms of film-forming conditions, rubbing conditions(e.g., rubbing strength), curing conditions (e.g., UV irradiationstrength and time), etc., and

[0247] (iv) a method wherein the undercoating layers different inmaterial and/or thickness are formed under oppositely disposed twoalignment control films contacting the liquid crystal 85, respectively.

[0248] Specific examples of the (chiral smectic) liquid crystal 85 usedin this example may include those used in First Embodiment describedabove.

[0249] Further, also in this embodiment, it is possible to used theliquid crystal device 80 in combination with polarizer(s) similarly asin the above-mentioned First Embodiment.

[0250] Next, a driving method for the display apparatus 100 according tothis embodiment will be described with reference to FIGS. 16 and 17.

[0251] Referring to FIG. 16, according to the driving method in thisembodiment, one frame period F0 is divided into three field periods F1,F2 and F3 and each of the field periods F1, F2 and F3 is further dividedinto two sub-field periods 1F and 2F (as shown at (a)).

[0252] The (liquid crystal) display device 80 is illuminated with aplurality of light source colors issued from the color light source 101while changing its color for F1, F2 and F3, respectively. In thisembodiment, the field periods corresponding to a red (R) display period,a green (G) display period and a blue (B) display period, respectively(as shown at (a) and (g)).

[0253] In synchronism with the respective color light emissions,switching of the color light concerned is performed. In this instance,in one (each) field period (e.g., F1), a higher luminance (red) image isdisplayed in the first sub-field period 1F and a lower luminance (red)image is displayed in the second sub-field period 2F by applyingvoltages Vg and Vs (as shown at (b), (c) and (d)).

[0254] The thus-displayed three color images (R, G and B images) in thethree field periods F1, F2 and F3, respectively, are visuallycolor-mixed in one frame period F0 to be recognized as a full-colorimage.

[0255] Each of the field periods F1, F2 and F2 may be divided into threesub-field periods 1F, 2F and 3F as shown in FIG. 17.

[0256] Referring to FIG. 17, in each field period (e.g., F1 corr. to red(R) image display period), image display for one color (e.g., red image)is performed in such a manner that a higher luminance (red) image isdisplayed at a transmitted light quantity Tx (R) in the first sub-fieldperiod 1F, a lower luminance (red) image is displayed at a transmittedlight quantity Ty (R) in the second sub-field period 2F and asubstantially no luminance (red) image is displayed at a transmittedlight quantity Tz (R) in the third sub-field period 3F (as shown at(a)-(d) in FIG. 17).

[0257] The number of the field periods constituting one frame period F0may be determined, e.g., depending on that of light source colors. Inthe case of the driving method shown in FIG. 17, one frame period F0 isconstituted by three field periods F1, F2 and F3 corresponding to Rdisplay period, G display period and B display period, respectively. Iffour light source colors of R, G, B and W (white) are employed, oneframe period F0 may be divided into four field periods F1 for R, F2 forG, F3 for B and F4 for W, respectively.

[0258] In this embodiment, in each field period (F1, F2 or F3 (or F4)),the higher and lower luminance (color) images displayed in the first andsecond sub-field periods 1F and 2F, respectively. These images may beidentical to each other except for their luminance levels. Further, theorder of display of these images may appropriately be changed, asdesired, within each field period so long as each of these images aredisplayed in one sub-field period (1F, 2F or 3F).

[0259] One color image displayed in each field period (F1, F2 or F3) mayappropriately be controlled depending on the corresponding light sourcecolor, thus improving a color reproducibility of a resultant full-colorimage displayed in one frame period.

[0260] With respect to the luminance of the higher and lower luminanceimages, the lower luminance image may preferably be controlled toprovide a luminance which is non-zero and at most ⅕ of a luminance givenby the higher luminance image. Such a luminance control may, e.g., beperformed by adjusting a light transmittance of the liquid crystal(display) device 80 through voltage application to the liquid crystal 85disposed between the pair of electrodes 82 a and 82 b. Morespecifically, when the liquid crystal 85 provides a V-T characteristicas shown in FIG. 7, a positive-polarity voltage (+V1) is applied fordisplaying the higher luminance image and a negative-polarity voltage(−V1) is applied for displaying the lower luminance image.

[0261] The image display operation in the display device 80 may beperformed, e.g., in a line-sequential manner.

[0262] In this embodiment, in the case where the display device 80 is anactive matrix-type liquid crystal device as shown in FIGS. 11 and 12,the liquid crystal apparatus 100 may be driven according to theabove-mentioned driving method shown in FIG. 14.

[0263] Referring to FIG. 14, at (a) is shown a waveform of gate voltageVg applied to one gate line Gi; at (b) is shown a waveform of sourcevoltage Vs applied to one source line Sj; at (c) is shown a waveform ofvoltage Vpix applied to the liquid crystal 49 at a pixel formed at anintersection of these gate and source line Gi an Sj; and at (d) is showna change in transmitted light quantity T at the pixel.

[0264] According to this driving method (FIG. 14), one frame period F0is divided into three field periods F1, F2 and F2 each of which isfurther divided into two sub-field periods 1F and 2F.

[0265] In this instance, when a frame frequency is 60 Hz, one frameperiod is ca. 16.7 msec. Each of the field periods F1, F2 and F2 is ca5.6 msec (16.7 msec/3) and each of the sub-field periods 1F and 2F isca. 2.8 msec (

5.6 msec/2).

[0266] The liquid crystal 49 used in this case exhibits a V-Tcharacteristic shown i FIG. 7.

[0267] Referring again to FIG. 14, in one sub-field period (e.g., 1F ofF1), one gate line Gi is supplied with a gate voltage Vg in a prescribed(selection) period Ton (as shown at (a)) and in synchronism with thegate voltage application, one source line Sj is supplied in theselection period Ton with a source voltage Vs (=V=Vx) based on apotential Vc (reference potential) of a common electrode 12 (FIG. 12)(as shown at (b)) At this time, a TFT 94 at the pixel concerned isturned on by the application of gate voltage g and the source voltage Vxis applied to the liquid crystal 49 via the TFT 94 and a pixel electrode95, thus charging a liquid crystal capacitor C1 c and a holdingcapacitor Cs.

[0268] In a non-selection period Toff other than the selection periodTon in the sub-field period 1F, the gate voltage Vg is applied to gatelines G1, G2, . . . , other than the gate line Gi. As a result, the gateline Gi is not supplied with the gate voltage V in the non-selectionperiod Toff, whereby the TFT 94 is turned off. Accordingly, the liquidcrystal capacitor C1 c and holding capacitor Cs hold the electriccharges charged therein, respectively, to provide the voltage Vx (=Vpix)through the sub-field period 1F 8as shown at (c)). The liquid crystal 49supplied with the voltage Vx through the sub-field period 1F provides atransmitted light quantity Tx substantially constant in the sub-fieldperiod 1F (as shown at (d)).

[0269] In the subsequent sub-field period 2F (of F1), theabove-described gate line Gi is again supplied with the gate voltage Vg(in Ton) (as shown at (a)) and in synchronism therewith, the source lineSj is supplied with a source voltage −Vs (=−V=−Vx) (of a polarityopposite to that of the source voltage Vs in 1F) (as shown at (b)),whereby the source voltage −Vx is charged in the liquid crystalcapacitor C1 c and holding capacitor Cs in Ton and kept in Toff (asshown at (c)).

[0270] As described above, the liquid crystal 49 shows the V-Tcharacteristic shown in FIG. 7, so that the resultant transmitted lightquantity T1 in the sub-field period 1F under application of thepositive-polarity source voltage Vx becomes large and the transmittedlight quantity T2 in the sub-field period 2F under application of thenegative-polarity source voltage −Vx becomes lower and close to zero. Asa result, in the entire field period F1, the resultant transmitted lightquantity becomes an average of Tx (=T1) and Ty (=T2). HOwever, bright(Tx) and dark (Ty) display operation can be alternately performed foreach sub-field period, thus improving resultant image qualities in thecase of effecting motion picture display. Further, the liquid crystal 49is supplied with the positive-polarity voltage Vx and thenegative-polarity voltage −Vx sub-field period by sub-field period in analternating manner, whereby a deterioration of the liquid crystal 49 incontinuous display is prevented.

[0271] In this case, the value (magnitude) of the positive-polaritysource voltage may be determined based on the V-T characteristic (FIG.7) of the liquid crystal 49 used and writing information for the pixelconcerned (i.e., an optical state or display information at the pixel).In this regard, the transmitted light quantity obtained through theentire field period F1 becomes an average of Tx and Ty as describedabove, so that when the liquid crystal 49 provides a remarkably low T2,the corresponding T1 (or V1 (=Vx) defining the T1 value) may be set tobe a larger value in order to obtain a desired transmitted lightquantity (average of Tx and Ty) in the entire field period F1.

[0272] The above-mentioned driving method for the display apparatus 100using the active matrix-type liquid crystal device 80 shown in FIG. 14may be applicable to a full-color image display in combination with thecolor light source 101 as shown in FIG. 16.

[0273] Referring to FIG. 16, in the (first) field period F1, the liquidcrystal device 80 is illuminated with red (R) light emitted from thecolor light source 101, whereby a black-and-white (monochrome) image onthe liquid crystal device 80 is recognized as a red image. Similarly, amonochrome image in the (second) field period F2 is recognized as agreen image by green (G) light emission from the color light source 101and in the (third) field period F3, a monochrome image is recognized asa blue image on the liquid crystal device 80 by blue (B) light emission.

[0274] These (three) color images in the field periods F1, F2 and F3 arevisually color-mixed in one frame period F0 to be recognized as afull-color image.

[0275] Such a full-color image display may also be performed by usingthe driving method shown in FIG. 17. As described above, in the drivingmethod of FIG. 17, each of the field periods F1, F2 and F3 is dividedinto three sub-field periods 1F, 2F and 3F.

[0276] Referring to FIG. 17, at (a) is shown a timing of emission ofrespective color lights from the color light source 101; at (b) is showna waveform of gate voltage Vg applied to one gate line (e.g., first gateline) G1; at (c) is shown a waveform of source voltage Vs applied to onesource line Si; at (d) is shown a waveform of voltage Vpix applied tothe liquid crystal 49 at a pixel formed at an intersection of these gateand source line G1 an Si; at (e) is shown a change in transmitted lightquantity T at the pixel; at (f) is shown a waveform of gate voltage Vgapplied to another gate line Gn; at (g) is shown a waveform of sourcevoltage Vs applied to another source line Sj; at (h) is shown a waveformof voltage Vpix applied to the liquid crystal 49 at a pixel formed at anintersection of these gate and source line Gn an Sj; and at (i) is showna change in transmitted light quantity T at the pixel.

[0277] According to this driving method (FIG. 17), the liquid crystaldevice 80 is driven in the same manner as in the driving method shown inFIG. 14 except that a voltage application operation in the thirdsub-field period 3F is performed in the following manner.

[0278] In the third sub-field period 3F, the gate line G1 is suppliedwith the gate voltage Vg while keeping a potential on the correspondingsource line Si at zero volt (as shown at (b) and (c) of FIG. 17),whereby the charges held in the liquid crystal and holding capacitors C1c and Cs are removed to place the liquid crystal 49 in a non-voltageapplication state, thus resulting in a transmitted light quantity Tz (R)of zero (as shown at (d) and (e)).

[0279] In this case, if the gate line Gn is the last gate line andscanned in the above-mentioned manner as in the gate line G1 (as shownat (f), (g), (h) and (i)), a resultant transmitted light quantitythrough the entire one field period F1 becomes an average of Tx (=T1),Ty (=T2) and Tz (=0).

[0280] In the subsequent field period F2, the green (G) light emissionmay preferably be performed in such a manner that the G emissionoperation is not effected immediately after the gate voltage Vgapplication to the last gate line Gn in the third sub-field period 3F ofthe field period F1 but effected after completely resetting the liquidcrystal 49 at the pixel along with the last gate line Gn in a black(dark) state. Consequently, a better color reproducibility can beattained.

[0281] According to this embodiment, both of the higher luminance imageand the lower luminance image are displayed in each of the field periodsF1, F2 and F2, so that the entire one field period (F1 or F2 or F3), acolor image having a luminance of an average of those of the higher andlower luminance images is displayed as described above with reference toFIGS. 14 and 16, thus enhancing the resultant luminance for each fieldperiod when compared with the conventional driving method as shown inFIG. 20 including non-image display period in each field period.Accordingly, the color light source 101 is not required to provide ahigher luminance, thus reducing power consumption.

[0282] In the case where the above-described driving method for imagedisplay is performed in a line-sequential manner, it is difficult toensure a scanning timing in synchronism with a light emission timing ofthe color light source 101 with respect to all the scanning (gate)lines, thus resulting in a deviation between these timings. For thisreason, as shown at (g) of FIG. 16 and at (i) of FIG. 17, e.g., when theliquid crystal device 80 is illuminated with a red (R) light emittedfrom the color light source 101 in the field period F1, with respect tothe last gate line, a monochrome image for the preceding blue image isdisplayed at a transmitted light quantity Ty (B) (as shown at (g) ofFIG. 16) or Tz (B) (as shown at (i) of FIG. 17).

[0283] In such a case, if the luminance of the monochrome image for theblue image is larger, the resultant color reproducibility is adverselyaffected by the luminance to be lowered.

[0284] In the present invention, however, the luminance of the lowerluminance image (i.e., Ty) is set to be non-zero and at most ⅕ of that(Tx) of the higher luminance image (as in the case of the driving methodof FIG. 16), thus minimizing the lowering in color reproducibility.

[0285] Particularly, in the case of the driving method of FIG. 17, theluminance (Tz (B)) is set to be zero, thus further effectivelysuppressing the lowering in color reproducibility.

[0286] Hereinbelow, the present invention will be described morespecifically based on Examples.

EXAMPLE 1

[0287] (Blank Cell A)

[0288] A blank cell A was prepared in the following manner.

[0289] A pair of 1.1 mm-thick glass substrates each provided with a 700Å-thick transparent electrode of ITO film was provided.

[0290] On each of the transparent electrodes (of the pair of glasssubstrates), a polyimide precursor for forming a polyimide having arecurring unit (PI-a) shown below was applied by spin coating andpre-dried at 80° C. for 5 min., followed by hot-baking at 200° C. for 1hour to obtain a 200 Å-thick polyimide film.

[0291] Each of the thus-obtained polyimide film was subjected to rubbingtreatment (as a uniaxial aligning treatment) with a nylon cloth underthe following conditions to provide an alignment control film.

[0292] Rubbing roller: a 10 cm-dia. roller about which a nylon cloth(“NF-77”, mfd. by Teijin K. K.) was wound.

[0293] Pressing depth: 0.3 mm

[0294] Substrate feed rate: 10 cm/sec

[0295] Rotation speed: 1000 rpm

[0296] Substrate feed: 4 times

[0297] Then, on one of the substrates, silica beads (average particlesize=2.0 μm) were dispersed and the pair of substrates were applied toeach other so that the rubbing treating axes were in parallel with eachother but oppositely directed (anti-parallel relationship), thuspreparing a blank cell (single-pixel cell) A with a uniform cell gap.

[0298] (Black Cell B)

[0299] A blank cell B was prepared in the same manner as in the case ofthe blank cell A except that one of the pair of glass substrate wasformed in an active matrix substrate provided with a plurality of a-SiTFTs and a silicone nitride (gate insulating) film and the other glasssubstrate was provided with a color filter including color filtersegments of red (R), green (G) and blue (B).

[0300] The thus prepared blank cell (active matrix cell) B having astructure as shown in FIG. 10 had a picture area size of 10.4 inchesincluding a multiplicity of pixels (800×600×RGB). (Liquid crystaldevices A and B) A liquid crystal composition LC-1 was prepared byblending the following mesomorphic (liquid crystal) compounds in theindicated proportions. Structural formula wt. parts

17

17

11.3

11.3

11.3

30

2

[0301] The thus-prepared liquid crystal composition LC-1 showed thefollowing phase transition series and physical properties.

[0302] (Iso: isotropic phase, Ch: cholesteric phase, SmC*: chiralsmectic phase)

[0303] Spontaneous polarization (Ps): 1.2 nC/cm² (30° C.) Cone angle{circle over (H)}: 23.7 degrees (30° C.)

[0304] Helical pitch (SmC*): at least 20 μm (30° C.)

[0305] The liquid crystal composition LC-1 was injected into each of theabove-prepared blank cells A and B in its isotropic liquid state andgradually cooled to a temperature providing chiral smectic C phase toprepare a (single-pixel) liquid crystal device A and a (active matrix)liquid crystal device B, respectively.

[0306] In the above cooling step from Iso to SmC*, each of the cells(devices) A and B was subjected to a voltage application treatment suchthat a DC (offset) voltage of −5 volts was applied in a temperaturerange of Tc+2° C. (Tc: Ch-SmC* phase transition temperature) whilecooling each device at a rate of 1° C./min.

[0307] The thus-prepared liquid crystal devices A and B were evaluatedin the following manner in terms of alignment state and optical responsecharacteristics for triangular wave and rectangular wave (for the liquidcrystal device A), and motion picture image display characteristic (forthe liquid crystal device B), respectively.

[0308] <Alignment State>

[0309] The alignment state of the liquid crystal composition LC-1 of theliquid crystal device A was observed through a polarizing microscope at30° C. (room temperature).

[0310] As a result, a substantially uniform alignment state such thatunder no voltage application, the darkest (optical) axis was somewhatdeviated from the rubbing direction and only one layer normal directionwas present over the entire cell (liquid crystal device A).

[0311] <Optical Response to Triangular Wave>

[0312] The liquid crystal device A was set in a polarizing microscopeequipped with a photomultiplier under cross nicol relationship so that apolarizing axis was disposed to provide the darkest state under novoltage application.

[0313] When the liquid crystal device A was supplied with a triangularwave (±5 volts, 0.2 Hz) at 30° C., a resultant transmitted lightquantity (transmittance) was gradually increased with the magnitude(absolute value) of the applied voltage under application of thepositive-polarity voltage. On the other hand, under application of thenegative-polarity voltage, a resultant transmitted light quantity waschanged with the applied voltage level but a maximum value of thetransmittance was ca. {fraction (1/10)} of a maximum transmittance inthe case of the positive-polarity voltage application.

[0314] <Optical Response to Rectangular Wave>

[0315] The optical response was evaluated in the same manner as in theabove case of using the triangular wave except for using a rectangularwave (±5 volts, 60 Hz) in place of the triangular wave.

[0316] As a result, under application of the positive-polarity voltage,the liquid crystal composition LC-1 was found to exhibit a sufficientoptical response thereto and provide a stable halftone state independentof a previous state. Further, also under application of thenegative-polarity voltage, an optical response (in terms oftransmittance) was confirmed similarly as in the case of thepositive-polarity application but the value thereof was ca. {fraction(1/10)} of that in the case of the positive-polarity voltage applicationwhen compared at an identical absolute value of the voltages. It wasalso confirmed that an average value of the resultant transmittance didnot depend on that in their previous states, thus attaining a goodhalftone image display.

[0317] Further, under application of the positive-polarity (rectangularwave) voltage application, when a brightening response time (RTb) (atime required to cause a transmittance change from the darkest state toa prescribed transmittance (under application of a prescribed voltage)or a transmittance of 90% based on the maximum transmittance) and adarkening response time (RTd) (a time required to cause a transmittancechange from a saturated transmittance state providing a prescribedhalftone image to a transmittance of 10% based on the maximumtransmittance) was measured.

[0318] The results are shown below. (Applied voltage) ca. 5 V ca. 1 VRTb (msec) 0.7 2.0 RTd (msec) 0.3 0.2

[0319] As apparent from the above results, the liquid crystalcomposition LC-1 shown a good high-speed responsiveness when comparedwith an ordinary nematic liquid crystal.

[0320] <Motion Picture Image Display>

[0321] The liquid crystal device B was driven according to theabove-mentioned driving method shown in FIG. 14 to evaluate a motionpicture quality in the following manner.

[0322] Three images (flesh-colored chart, sightseeing information(guide) board, and yacht basin) were selected from Hi-vision standardimages (still images) of BTA (Broadcasting Technology Association) andrespective central portions (each corr. to 432×168 pixels) of theseimages were used as three sample images.

[0323] These sample images were moved at a speed of 6.8 (deg/sec)corresponding to that of an ordinary TV program to form motion pictureimages, which were outputted from a computer (as an image source) at apicture rate of 60 frames per 1 sec. in a progressive (sequentialscanning) mode, thus evaluating a degree of image blur particularly at aperipheral portion of the outputted images.

[0324] Specifically, evaluation of the images was performed by 10amateur viewers in accordance with the following evaluation standard.

[0325] 5: Clear and good motion picture image with no peripheral imageblur was observed.

[0326] 4: Slight peripheral image blur was observed but was practicallyof no problem.

[0327] 3: Peripheral image blue was observed and it was difficult torecognize fine or small characters.

[0328] 2: Remarkable peripheral image blur was observed and it wasdifficult to recognize large characters.

[0329] 1: Remarkable image blue was observed over the entire picturearea and the original sample images were little recognized.

[0330] The drive of the liquid crystal device B was first performed at adisplay rate of 60 frames per 1 sec. in a frame-inversion drive schemewithout dividing one frame period into a plurality of field periods.

[0331] As a result, a slight peripheral image blur of the motion pictureimages was observed but was at a practically fully acceptable levelbetween “3” or “4”.

[0332] Then, the liquid crystal device B was driven according to thedriving method shown in FIG. 14 wherein one frame period ca. 16.7 msec)was divided into two field periods (each ca. 8.3 msec) and apositive-polarity voltage was applied in the first field period (Ton=ca.13.8 psec) and a negative-polarity voltage (having a voltage level(absolute value) identical to that of the positive-polarity voltage) wasapplied in the second field period (Ton=ca. 13.8 psec) to substantiallyprovide a (field) frequency of 120 Hz (=60 Hz×2).

[0333] As a result, excellent motion picture images providing apractically sufficient luminance and free from flickering and image blurwere observed at a level of “5”.

[0334] In this regard, when the evaluation was performed with respect toa commercially available CRT monitor, all the viewer evaluated theresultant images as a level of “5”. Further, in the case of acommercially available (conventional) TFT liquid crystal panel(generally providing a response time of several ten mill-seconds), theevaluation result was a level between “2” and “3”.

EXAMPLE 2

[0335] A (single-pixel) liquid crystal device C and an (active matrix)liquid crystal device D were prepared in the same manner as in theliquid crystal devices A and B prepared in Example 1, respectively,except that each of the 200 Å-thick polyimide alignment control film(PI-a) was changed to a 50 Å-thick alignment control film of a polyimidehaving a recurring unit (PI-b) shown below and that the average particlesize (2.0 μm) of the silica beads was changed to 1.4 μm.

[0336] When the thus-prepared liquid crystal devices C and D wereevaluated in the same manner as in the liquid crystal devices A and B(used in Example 1), respectively, these liquid crystal devices C and Dprovided substantially similar characteristics and performances to thoseof the liquid crystal devices A and B, respectively.

[0337] Further, similarly as in Example 1, under application of thepositive-polarity (rectangular wave) voltage (to the liquid crystaldevice C), a brightening response time (RTb) and a darkening responsetime (RTd) was measured.

[0338] The results are shown below. (Applied voltage) ca. 4 V ca. 1 VRTb (msec) 0.6 1.7 RTd (msec) 0.2 0.2

[0339] As apparent from the above results, the liquid crystalcomposition LC-1 used in the liquid crystal device C shown a goodhigh-speed responsiveness when compared with an ordinary nematic liquidcrystal.

EXAMPLE 3

[0340] A (single-pixel) liquid crystal device E and an (active matrix)liquid crystal device F were prepared and evaluated in the same manneras in the devices A and B used in Example 1, respectively, except thatthe anti-parallel rubbing treatment was changed to a parallel rubbingtreatment (so that two rubbing treating axes were directed in anidentical direction and in parallel with each other), whereby thefollowing results were obtained.

[0341] <Alignment State>

[0342] When the alignment state of the liquid crystal composition LC-1of the liquid crystal device E was observed through a polarizingmicroscope at 30° C., a substantially uniform alignment state such thatunder no voltage application, the darkest (optical) axis was somewhatdeviated from the rubbing direction and only one layer normal directionwas present over the entire cell (liquid crystal device E). Thealignment state was a co-present state of C1 alignment region and C2alignment region (1:1).

[0343] <Optical Response to Triangular Wave>

[0344] When the liquid crystal device E was supplied with a triangularwave (±5 volts, 0.2 Hz) at 30° C., a resultant V-T characteristic overthe entire cell was similar to that of the liquid crystal device A usedin Example 1. More specifically, in the C1 alignment region, adomain-less switching was observed at a transmittance of at most ca. 50%on voltage increase but an inverted domain was observed when the appliedvoltage was further increased. In the C2 alignment region, a domain-lessswitching was observed until the applied voltage reached the saturationvoltage. Further, an identical transmittance (transmitted lightquantity) was given at a lower applied voltage in the C2 alignmentregion than that in the C1 alignment region.

[0345] <Optical Response to Rectangular Wave>

[0346] The optical response characteristic of the liquid crystal deviceE under the rectangular wave application was similar to that of theliquid crystal device A used in Example 1. Thus, it is possible toeffect an analog-like gradational display based on amplitude modulationaccording to an active matrix driving scheme using TFTs. When the C1 andC2 alignment regions were observed separately, similarly as in the caseof the triangular wave application, a prescribed transmittance(transmitted light quantity) in the C2 alignment region was given at anapplied voltage lower than that in the case of the C1 alignment region.

[0347] Further, when the liquid crystal device E was subjected tomeasurement of a brightening response time (RTb) and a darkeningresponse time(RTd), the following results were obtained. (Appliedvoltage) ca. 5 V ca. 1 V RTb (msec) 0.6 1.8 RTd (msec) 0.3 0.2

[0348] As apparent from the above results, the liquid crystalcomposition LC-1 used in the liquid crystal device E showed a goodhigh-speed responsiveness when compared with an ordinary nematic liquidcrystal.

[0349] <Motion Picture Image Display>

[0350] When the liquid crystal device F was evaluated as to the motionpicture image quality (according to the active matrix driving at 60 Hzand 120 Hz similarly as in Example 1), the resultant motion pictureimages were displayed at a practically sufficient luminance with aperipheral image blur similarly as in Example 1 and the degree of themotion picture image quality was at a level of “5”.

EXAMPLE 4

[0351] (Blank Cell G)

[0352] A blank cell G was prepared in the following manner.

[0353] A pair of 1.1 mm-thick glass substrates each provided with a 700Å-thick transparent electrode of ITO film was provided.

[0354] On each of the transparent electrodes (of the pair of glasssubstrates), a commercially available polyimide alignment film-formingsolution for a TFT liquid crystal device (“SE-7992”, mfd. by NissanKagaku K. K.) was applied by spin coating and pre-dried at 80° C. for 5min., followed by hot-baking at 200° C. for 1 hour to obtain a 50Å-thick polyimide film.

[0355] Each of the thus-obtained polyimide film was subjected to rubbingtreatment (as a uniaxial aligning treatment) with a nylon cloth underthe following conditions to provide an alignment control film.

[0356] Rubbing roller: a 10 cm-dia. roller about which a nylon cloth(“NF-77”, mfd. by Teijin K. K.) was wound.

[0357] Pressing depth: 0.3 mm

[0358] Substrate feed rate: 10 cm/sec

[0359] Rotation speed: 1000 rpm

[0360] Substrate feed: 4 times

[0361] Then, on one of the substrates, silica beads (average particlesize=1.4 μm) were dispersed and the pair of substrates were applied toeach other so that the rubbing treating axes were in parallel with eachother and directed in an identical direction (parallel relationship),thus preparing a blank cell (single-pixel cell) G with a uniform cellgap.

[0362] (Black Cell H)

[0363] A blank cell H was prepared in the same manner as in the case ofthe blank cell A except that one of the pair of glass substrate wasformed in an active matrix substrate provided with a plurality of a-SiTFTs and a silicone nitride (gate insulating) film and the other glasssubstrate was provided with a color filter including color filtersegments of red (R), green (G) and blue (B).

[0364] The thus prepared blank cell (active matrix cell) H having astructure as shown in FIG. 10 had a picture area size of 10.4 inchesincluding a multiplicity of pixels (800×600×RGB).

[0365] (Liquid Crystal Devices G and H)

[0366] The liquid crystal composition LC-1 prepared in Example 1 wasinjected into each of the above-prepared blank cells G and H in itsisotropic liquid state and gradually cooled to a temperature providingchiral smectic C phase to prepare a (single-pixel) liquid crystal deviceG and a (active matrix) liquid crystal device H, respectively.

[0367] In the above cooling step from Iso to SmC*, each of the cells(devices) G and H was subjected to a voltage application treatment suchthat a DC (offset) voltage of −5 volts was applied in a temperaturerange of Tc±2° C. (Tc: Ch-SmC* phase transition temperature) whilecooling each device at a rate of 1° C./min.

[0368] The thus-prepared liquid crystal devices G and H were evaluatedin the same manner as in Example 1 in terms of alignment state andoptical response characteristics for triangular wave and rectangularwave (for the liquid crystal device G), and motion picture image displaycharacteristic (for the liquid crystal device G), respectively.

[0369] <Alignment State>

[0370] When the alignment state of the liquid crystal composition LC-1of the liquid crystal device G was observed, a substantially uniform C2alignment state such that under no voltage application, the darkest(optical) axis was somewhat deviated from the rubbing direction and onlyone layer normal direction was present over the entire cell (liquidcrystal device G).

[0371] <Optical Response to Triangular Wave>

[0372] When the liquid crystal device G was supplied with a triangularwave (±5 volts, 0.2 Hz) at 30° C., a resultant V-T characteristic wassimilar to that of the device A used in Example 1. Further, adomain-less switching was observed until the applied voltage reached asaturation voltage.

[0373] <Optical Response to Rectangular Wave>

[0374] The optical response characteristic of the liquid crystal deviceG under the rectangular wave application was similar to that of theliquid crystal device A used in Example 1. Thus, it is possible toeffect an analog-like gradational display based on amplitude modulationaccording to an active matrix driving scheme using TFTs.

[0375] Further, when the liquid crystal device G was subjected tomeasurement of a brightening response time (RTb) and a darkeningresponse time(RTd), the following results were obtained. (Appliedvoltage) ca. 3 V ca. 0.6 V RTb (msec) 0.5 1.6 RTd (msec) 0.2 0.2

[0376] As apparent from the above results, the liquid crystalcomposition LC-1 used in the liquid crystal device G showed a goodhigh-speed responsiveness when compared with an ordinary nematic liquidcrystal.

[0377] <Motion Picture Image Display>

[0378] When the liquid crystal device H was evaluated as to the motionpicture image quality (according to the active matrix driving at 60 Hzand 120 Hz similarly as in Example 1), the resultant motion pictureimages were displayed at a practically sufficient luminance with aperipheral image blur similarly as in Example 1 and the degree of themotion picture image quality was at a level of “5”.

EXAMPLE 5

[0379] A color liquid crystal display apparatus was prepared by using a(active matrix) liquid crystal device prepared in the same manner as inthe device B used in Example 1 except for omitting the color filter andalso using a backlight device 101 (as a color light source) as shown inFIG. 18 in combination.

[0380] The backlight device 101, as shown in FIG. 18, included threesets of closed circuits for emitting three colors of red (R), green (G)and blue (B). Each of the closed circuits was comprised of a powersource 110, a transistor 111 and seven LEDs (light-emitting diodes) 112and was electrically connected with a wave generator 113 so as to beappropriately turned on or off, thus allowing a successive emission ofthe respective lights (of R, G and B).

[0381] As materials for the respective light-source lights, CaAlAs wasused for R and GaN was used for G and B.

[0382] For emission of the respective color lights, a voltage was set toca. 14 volts for R and ca. 25. volts for G and B and a current was setto at most 20 mA.

[0383] The above-prepared liquid crystal display apparatus was drivenaccording to a driving method shown in FIG. 16 (driving voltage=±5volts, frame-frequency=60 Hz, f₀=ca. 16.7 msec, f1=ca. 5.6 msec, 1F=ca.2.8 msec) to evaluate a (maximum) panel luminance in a white imagedisplay state and color purities of the respective color lights (R, G,B).

[0384] As a result, the resultant panel luminance was 110 cd/m².Further, with respect to the color purities were gradually somewhatchanged in color tint in order of the scanning lines but were at a levelbeing practically of no problem.

[0385] Separately, by using the (single-pixel) liquid crystal device Aprepared in Example 1, an optical response to a rectangular wave wasevaluated in the same manner as in Example 1 except for changing thefrequency from 60 Hz to 180 Hz, whereby a resultant optical responsecharacteristic was similar to that obtained in Example 1.

Comparative Example 1

[0386] A (single-pixel) liquid crystal device I and an (active matrix)liquid crystal device J were prepared in the same manner as in Example 1except that the liquid crystal composition LC-1 was changed to a liquidcrystal composition LC-2 prepared below and the DC offset voltage (of −5volts) was changed to a DC offset voltage of +3 volts.

[0387] The liquid crystal composition LC-2 was prepared by mixing thefollowing compounds in the indicated proportions. Structural formula wt.parts

10

80

5

[0388] The thus-prepared liquid crystal composition LC-2 showed thefollowing phase transition series and physical properties.

[0389] Spontaneous polarization (Ps): 1.8 nC/cm² (30° C.)

[0390] Cone angle {circle over (H)}: 23.7 degrees (30° C.)

[0391] Helical pitch (SmC*): at least 20 μm (30° C.)

[0392] The thus-prepared liquid crystal device I was evaluated in thesame manner as in Example 1 in terms of alignment state and opticalresponse characteristics for triangular wave and rectangular wave.

[0393] <Alignment State>

[0394] The alignment state of the liquid crystal composition LC-2 of theliquid crystal device I was observed through a polarizing microscope.

[0395] As a result, a substantially uniform alignment state such thatunder no voltage application, the darkest (optical) axis wassubstantially aligned with (in parallel with) the rubbing direction andonly one layer normal direction was present over the entire cell (liquidcrystal device I).

[0396] <Optical Response to Triangular Wave>

[0397] The liquid crystal device I was set in a polarizing microscopeequipped with a photomultiplier under cross nicol relationship so that apolarizing axis was disposed in alignment with the rubbing direction toprovide the darkest state under no voltage application.

[0398] When the liquid crystal device I was supplied with a triangularwave (±5 volts, 0.2 Hz) at a temperature (T) below the Ch-SmC* phasetransition temperature (Tc) by 10° C. (Tc-T=10° C.), a resultanttransmitted light quantity (transmittance) was gradually increased withthe magnitude (absolute value) of the applied voltage under applicationof the positive-polarity voltage. On the other hand, under applicationof the negative-polarity voltage, a resultant transmitted light quantitywas substantially not changed from that in a black state (the darkeststate) under no voltage application. Further, when the applied voltagewas removed in the white (bright) state under the positive-polarityvoltage application, switching from the white state to the black statewas confirmed.

[0399] <Optical Response to Rectangular Wave>

[0400] The optical response was evaluated in the same manner as in theabove case of using the triangular wave except for using a rectangularwave (±5 volts, 180 Hz) in place of the triangular wave.

[0401] As a result, only under application of the positive-polarityvoltage, the liquid crystal composition LC-2 was found to exhibit asufficient optical response thereto, whereby it was possible to change aluminance level depending on a voltage level of the applied(positive-polarity) voltage.

[0402] Further, under application of the positive-polarity (rectangularwave) voltage (saturation voltage=ca. 5 volts), a brightening responsetime (RTb) (a time required to cause a transmittance change from thedarkest state to a transmittance of 90% based on a prescribedtransmittance (under application of a prescribed voltage) and adarkening response time (RTd) (a time required to cause a transmittancechange from a saturated transmittance state (maximum transmittance) to atransmittance of 10% based on the maximum transmittance) was measured.

[0403] The results are shown below. (Applied voltage) ca. 5 V RTb (msec)0.6-0.9 RTd (msec) 0.2-0.3

[0404] As apparent from the above results, the liquid crystalcomposition LC-2 shown a good high-speed responsiveness and accordinglywas confirmed to be applicable to the serial driving scheme using thecolor light source of R, G and B as in Example 5.

[0405] On the other hand, the above-prepared (active matrix) liquidcrystal J was used for preparing a color liquid crystal displayapparatus in combination with the backlight device 101 (as a color lightsource) similarly as in Example 5 and was similarly evaluated as inExample 5 according to the serial driving scheme using the color lightsource of R, G and B while applying a driving voltage of ±5 volts.

[0406] As a result, the liquid crystal device J provided a uniform colorreproducibility at the entire panel surface but the resultant panelluminance was 100 cd/m² lower than that (110 cd/m²) of the liquidcrystal device B used in Example 5.

EXAMPLE 6

[0407] A color liquid crystal display apparatus was prepared and drivenin the same manner as in Example 5 except that the driving method (FIG.16) was changed to that shown in FIG. 17 (driving voltage=±5 volts).

[0408] As a result, the color liquid crystal display apparatus showed agood color reproducibility.

[0409] When the (single-pixel) liquid crystal device A prepared inExample 1 was evaluated as to an optical response to a rectangular wave(±5 volts, 270 Hz), the resultant optical response characteristic wassimilar to that obtained in Example 1.

[0410] As described hereinabove, according to the present invention, itis possible to provide a liquid crystal device using a chiral smecticliquid crystal capable of allowing a high-speed responsiveness andcontrol of gradation levels while retaining excellent motion pictureimage qualities and a high luminance.

[0411] Further, in the case where in one sub-field, a higher luminanceimage is displayed in at least one sub-field period and a lowerluminance image is displayed in at least one another sub-field period,the resultant image displayed through the entire one sub-fieldcorresponding to an image having a luminance of an average of those ofthe higher and lower luminance images, thus improving the luminancelevel compared with the conventional driving scheme including anon-image display period. As a result, it is unnecessary to employ acolor light source providing a higher luminance, thus reducing powerconsumption.

[0412] Further, in the case of effecting image display in aline-sequential manner, a lowering in color reproducibility can beeffectively suppressed.

1-37. (Cancelled)
 38. A display apparatus comprising: a liquid crystaldevice including a pair of substrates and a liquid crystal disposedbetween the pair of substrates to form a plurality of pixels; controlmeans for effecting a plurality of displaying operations at each pixel,each displaying operation including a sequence of a first operation anda second operation, wherein the liquid crystal exhibits avoltage-transmittance characteristic of showing a first transmittance inresponse to zero voltage, and a second transmittance and a thirdtransmittance which are different from each other and both being higherthan the first transmittance in response to positive and negativevoltages of an identical level, and a first drive voltage waveform and asecond drive voltage waveform which are identical in shape to but aredifferent in polarity from each other are sequentially applied to theliquid crystal in the first and second operations, respectively, theliquid crystal device thereby displaying an identical image at mutuallydifferent levels of non-zero luminances in the first and secondoperations, respectively.
 39. An apparatus according to claim 38,wherein one of the first and second luminances is smaller than ⅕ of theother luminance.
 40. A liquid crystal apparatus comprising: a liquidcrystal device comprising a matrix of pixels; and a drive circuit fordriving the liquid crystal device to effect desired gradational display,wherein each pixel is supplied with a driving signal from the drivecircuit, the driving signal including in a first period a first voltagefor providing a prescribed gradational image and in a second period asecond voltage for providing a light quantity smaller than a lightquantity in the first period but larger than zero.
 41. An apparatusaccording to claim 40, wherein the liquid crystal device includes a pairof substrates to sandwich a liquid crystal, and one of the pair ofsubstrates comprises a substrate provided with active devices eachelectrically connected with an electrode portion defining each of thepixels, and the liquid crystal device is driven by the drive circuit toeffect active matrix drive allowing analog-like gradational display. 42.A display apparatus comprising: a liquid crystal device comprising aplurality of pixels; and control means for effecting a plurality ofdisplaying operations within one frame period to the liquid crystaldevice, each displaying operation including a sequence of a firstoperation and a second operation, wherein the liquid crystal devicedisplays an image at a first luminance in the first operation, andperforms a second luminance in the second operation which level isnon-zero and lower than a level of the first luminance.
 43. A displayapparatus comprising: a liquid crystal device comprising a plurality ofpixels; and control means for effecting a plurality of displayingoperations within one frame period to the liquid crystal device, eachdisplaying operation including a sequence of a first operation and asecond operation, wherein the liquid crystal device displays an image ata first luminance in the first operation, and displays the image at asecond luminance in the second operation which level is non-zero andlower than a level of the first luminance, and receives the same displaydata in the first and second operation.